• Potions that provide permanent health/mana boosts use a special independent field within the player character file.  I have not yet checked whether this can be applied to other stats, though it looks like it may be possible. 
• Skills can target items within player inventory, but the only built-in filter for this functionality is "any item" and "unidentified item".  In theory, I could use "unidentified item" to handle filtering (since lore-wise unidentified items are enchanted with Ember), but that would put a serious crimp on the skill "flavor".   
• The effect data for shrines is not stored within the shrine object itself.  I suspect it is stored somewhere in the terrain layouts instead, but I am not familiar enough with that format to be certain.  I was hoping to examine the internal effects of Enchantment shrines to help derive the item destruction effect. 

Spoiler (hover to show)

So, I agree with Anarch about the two possible implementations: consumable or UI.

The consumable item option would be fine since TL1 is single player; you don't have to worry about multiplayer compatibility with this mod.  The only hard part is that, if setting the base file to consumable doesn't change all the others, you'd have to manually change all the different ember items to 'consumable'.  Then you'd want to add an effect to each ember to make it add to a custom stat (like Anarch said), and you'd probably want to modify the value by quality of ember (+1 for a speck, +5 for a flawless perhaps?)  That might take a little time, but not too much.

The other option, the inventory slot, is done through the UI and the Slots/Containers editor.  This wouldn't require a skill.  Instead, you'd use a logic group to remove the ember and add +1 (or whatever value you wish) to a custom stat that records how much ember you've eaten.  This solution might take a little more time.

I also agree about using a custom stat.  This way, you can also create a graph to control how much of a stat boost the character should get from having eaten a certain amount of ember.  Maybe you want it take 1 Core ember to give +2 Str, but 100 Core ember to give +5 Str (just for example).  You can do that by having an Effect set to the character that gives a bonus to Str based on the (just a suggestion) Core_Ember_Eaten stat.


Now, I'm assuming that you asked...

Quote

1. Is there a way to make a skill able to target certain kinds of non-equipment items, but not others?  If so, how?
2. Is there a way to make a single skill behave differently depending on the name of its target?  If so, how?
3. Is there a way to make a skill override an entity's internal properties (for example, the "invincible" flag)?  If so, how?
4. Is there a way to change a skill in TL1 so it uses stats instead of levels as a prerequisite?  If so, how?
5. Is there a way to make a skill check the properties of the current area, such as whether town-portals are allowed?  If so, how? 

...because that's the setup you imagined for creating an 'ember consumption' mechanic that adds to your stats.  But like Anarch and I have outlined above, I don't think #1-4 are actually necessary.

Just add one effect to your custom class per ember effect (so, one effect that adds Str per Core Ember eaten, another for Fire Res based on Fire Ember eaten, etc).  You'll also want one custom stat per effect, so Fire_Ember_Eaten, Core_Ember_Eaten, etc.



As for #5, I'm not sure.  Why do you want to do this?  There may be an alternate method.

So, yes, you should be able to (stylishly) achieve this class' functionality using TorchEd.

#3  Yes.  This should be simple, though depending on what exactly you're trying to do this could take anywhere from a few minutes to many hours of work.

#4  Yes.  You can do this using the UI and Logic Groups.  You basically hijack the skill invest button in the skill pane UI and add stat requirements that must be met before the button becomes functional.  You'll also need to add an additional stat for each skill to track the level of skill investment (so you can give each level a different stat requirement).

#5  ....yes.   But my unfamiliarity with TorchEd makes me unable to speculate on how much time this would take.  I know how to do it in GUTS.  Since the two editors are 95% identical, I'd assume it's possible in TL1.  This might be a fairly complicated procedure.

Modifying text files is typically 10x faster than using the editors, at least for skills, unit files, spawnclasses and items. 

Here, check out the GUTS tutorial for an example.  If Torched has something similar it won't be difficult at all.

As far as I know re: using the identify scroll skill as a template, it won't work.  The identify skill is a coded function which doesn't actually work the way skills do.  It's an Effect (a class of function in TL1), but doesn't have any options to change the target or the effect. 

Take a look at the two options for this setup that Anarch and I suggested.

#3 is very easy as you've described.  It's just a basic passive skill.  Just remember to set it to remove the effect on Event_End.

And yeah, #5 is definitely a possibility.  I would look to see if you can just add an effect to a dungeon in the Dungeon editor.  You can do this in TL2.  You can use this effect to toggle a custom stat depending on whether teleporting is allowed in the dungeon.  Maybe toggle on in regular zones, toggle off in others.  Then, you set a Stat_Watcher (Stat_Requirement) to your Teleport skill that only allows you to use the skill in zones where teleporting is allowed.

If I had TL2 unpacked onto my computer right now I'd look in the Unit files for a Commander Vale or some similar NPC that's probably set to Invincible and see what the boolean's called in the text file. 

To declare a dynamic stat, you just add it in the Stats Editor and give it the name you think is most likely used by the game.  You might try several different names if the first one does not work.