Howdy all.
I'm sort of in charge of dictating enemy stat changes, but I will list some other skills I offer that I can do without TF (I will assume anything I can accomplish inside of TF can already be done). Many of them will be redundant, but a handful may prove useful.
Changing initial character stats: This skill seems well-covered already.
Changing weapon stats: This includes power, price, and one special effect (slow, chaos, strong against "magic" enemies, "Demi" against vulnerable enemies, death, slumber, 4x damage critical, etc), but other abilities are discussed below.
Changing armor/helmet stats: This includes defense, price, and one special effect (haste, safe, chaos protection, etc), but other abilities are discussed below.
I can dictate certain stat changes for weapons, armor, helmets, and a handful of accessories: Power, Speed, Stamina, Hit, Evade, Magic, and Magic Defense. However, any stats I change must be changed by the same amount. The stat can range from -128 (which would nullify any chosen stats) to +127 (which would max out any chosen stats). The maximum number of different stat combination changes allowed is 127 (or possibly 128 if you count the "default" action of no stat changes, which I've never tried changing). You can make useful accessories this way (because let's face it, +10 STR is worthless compared when compared to the effect of overpowering accessories, like PrismSpecs). This was a pretty exciting discovery for me!
I can change who can use certain equipment.
I can change elemental protection and scale that protection between 0% and 75% (0%, 17%, 29%, 38%, 45%, 50%, etc). I can do this with multiple elements, but all elements must be changed by the same amount. Making a character "weak" to an element under any circumstance is not truly possible, but you can make them relatively weak by having alternative armor protect a little bit against all elements, and then the next armor would provide either no protection (weak) or heavy protection (strong) against other elements. These changes can done in addition to potentially one "absorbed" element (so an armor could absorb fire, be "neutral" against lightning and shadow via small elemental resistance, and then be "weak" to water). Absorption is available for armor/helmets only, but elemental resistance is available to ALL equipment.
I can change how certain items and equipment can be used/sold/etc.
I can change the price, power, and sometimes even the type of effect by a certain item (but the animation will probably be wrong).
I can change store information, but that ability is redundant.
Character tech (limited): I can change their power and TP cost. I can also sometimes change their effects, but the animations will still be wrong. Still, I found changing power and TP cost to be a little useful in previous work!