Can one create spells, enchanted devices etc. that work on a narrower range of targets than would be normally permitted by the guidelines? For example ... "Cat of outlandish size" that works like Beast of Outlandish size but only works on cats?
Initially, I thought "obviously yes". While generally pointless, there are cases when it would make sense, for example to benefit from a magical focus in cats when you create an enchanted collar with said effect for your favourite cat.
However, I now realize that it would allow a magus to do some really sneaky detection stuff. For example, imagine you want to ascertain whether a person has the Gift. You can cast a Base 10 effect to explicitly detect it (The numbness of the Gift, Apprentices p.33). But if you allow "restricted targets" you could also cast "Pink Dot for the Gifted": a Base 1,MuIm (note, it's not just much lower level, it's not an Intellego spell either) effect that makes a pink dot appear on the subject's forehead, and only works on Gifted targets. This is something I dislike immensely.
Any ideas?