How do you delete a set of macros that may or maynot be created during a build run?

[ambalboa]

I've been thinking, since I am using these temp. macros to do build rules, I suppose I need to create all of them, right? I guess when the filename is not found, I should create/set the temp. macro anyway but with a different value. If I have a build rule that evaluates a macro, and that macro doesn't exist, an error would occur? If so, I'll just figure out a way to correct this. Sorry and thanks.