A few things:
1) Creating tomes like this is all good, but if you do it a ton, you could make your map slower. The items are not cleaned up properly (if they use the tome models, they actually just shrink into dots and you can see them forever). Just keep that in mind since it could suck if you over use this trick.
2) A mana ability with 200 levels doesn't actually work. I don't know the exact details, but levelling the item abilities that add max health or mana do not actually change values when they level up. It is a bug. There are a bunch of abilities like this, but these two are pretty big ones.
There are two main ways you can do this:
1) Make a system where you have a single mana ability that each adds:
1, 2 ,4 ,8, 16, 32, 64, 128 ... doubling each time.
You then have to use a hashtable or unit indexer to keep track of how much is added to each unit. You then add and remove the proper abilities to make them add up to the value you need. Once you get up to around 10 abilities, you can have any number all the way up to 1000. I can go into more detail if you want.
2) There is a sort of related bug with the health and mana abilities. They don't change when you increase the level of the ability with triggers, but when you remove them after increasing the level, it removes the current level value health / mana instead of the level 1 amount. This is exploitable as a tool.
Basically, you create a mana ability where it has level 1 adds 0 mana, and level 2 add -10 mana (could be -100 to add 100 at a time, etc). When you want to add the mana to a unit, you add the ability, increment the ability level for the unit, then remove the ability. It will remove -10 mana which adds it instead. You can use this to add any amount of health or mana without spamming tomes or anything. It is probably the best solution for this.
Note that you can add negative values for ability stats by holding shift and then editing the value. Don't know if you know that or not, but I think you need it for this method.
