Higher target levels used to affect lower target levels?

The answer to that question is at least yes in some cases.

Specifically, if you cast a spell with a "Group" target, it can be used to affect a single individual (up to the mass of 10 standard individuals). Additionally, if you cast a spell with a Target of "Part" you can affect a Part up to the size of a single Individual, which means you can affect a single individual if you choose. And it seems likely that you could affect a "Room" with a target of "Boundary" if you chose (not 100% certain of this one).

But the question I have is, if you cast a spell with a target "Group", can you affect a "Part"?

If I have a spell that turns a "Group" of rocks red, could I instead turn a large "Part" of a stone wall red with the same spell?

Your thoughts on this issue are appreciated?

I'd think not. Look at the definition of group. It talks about a discrete group of individuals. While a single individual is a discrete group of one, part of an individual is not a discrete group of individuals [/serf's parma]

I concur.

Think of it like this: you can't really use higher level targets to affect lower level targets (eg. group for part or ind), but you can use a group spell to affect a group of 1 (a very small group) in the same way you can use a structure spell to affect a hovel with a single room. A room should fit the description of a clearly defined boundary, so that should work just fine. However, using a structure spell to affect 1 of several rooms in a building doesn't work.

As for the wall - if it is a wall composed of several individual stones, then your group spell would work (as well as the part spell, since it is a part of the singular wall...)