Houserule for heighten Spell - How about that?

[With a box]

Would you allow use heighten spell to increase spell limit in spell discription?
like heighten shadow evocation to 6lv to put 5th level evocation spell in it
or heighten invoke magic to 10lv to teleport out of it (well it need epic feat, but i ignored that)
or increase the damege cap of spells

[Nettlekid]

I would allow this as a DM. The Shadowcraft Mage already works like this on a more limited scale, so there's precedent of a sort. Maybe for balance make it more like two Heightened levels raises caps by one level. But I like the idea.

[Doc_Maynot]

I can think of an issue stemming from either Earth Spell, Mind Mage's Compensation, or DMM: Heighten

[StreamOfTheSky]

Would you allow use heighten spell to increase spell limit in spell discription?
like heighten shadow evocation to 6lv to put 5th level evocation spell in it
or heighten invoke magic to 10lv to teleport out of it (well it need epic feat, but i ignored that)

I wouldn't allow that level of customization to the shadow line of spells, no. Besides, much like enchantments, shadow spells already have a lot riding on the save, so they're one of the types of spells that you'd actually want to heighten (if the idea of paying higher slots just for a paltry save bonus is appealing to you under any circumstance) already.

What I do houserule for the feat is as follows:

Heighten Spell [Metamagic, Wizard]
Add the following:
1) The damage dice cap for any direct damage spell the feat is used on is extended to what would be appropriate for that level (example: a fireball at spell level 5 would cap at CL 15 and 15d6 damage). See DMG p. 36 for dice caps.
2) You can use the feat with any "series" type summoning spell (summon monster/nature's ally/undead/etc...) to gain the benefit of the higher level version. For example, Summon Monster I could be heightened to spell level 6 and count as Summon Monster VI.

The first one just allows for customization of direct damage spells, the weakest class of spells there are, and I'm kind of surprised WotC never published such a rule. The 2nd might be a bit overpowered, but prepared casters generally won't care; it's basically just making SM I way more versatile for a sorcerer and other prepared casters, practically works like augmenting astral construct for them. No player's ever taken Heighten Spell in my games, so I haven't gotten to playtest it.