Mana Unbound
This a really simple mod, that allows you to have more than 600 mana, by removing the 400 cap from statManaMax2.
How it works
All this mod does, is replace a single instruction in Player.Update using tModLoader's built-in IL patcher.
In the part that looks like this:
IL_2DEC: ldarg.0
IL_2DED: ldfld int32 Terraria.Player::statManaMax2
IL_2DF2: ldc.i4 400
IL_2DF7: ble.s IL_2E04
IL_2DF9: ldarg.0
IL_2DFA: ldc.i4 400
IL_2DFF: stfld int32 Terraria.Player::statManaMax2
ldc.i4 400 is replaced with ldc.i4 2147483647 which is int.MaxValue. Since statManaMax2 can never be greater than this value, the last three instructions are always skipped.