if the app already exists elsewhere (and Apple doesn't care), then it can work out. E.g., for many years, i've kept my TextWrangler.app located here:
/Users/halito/Applications/TextWrangler 3.1/TextWrangler.app
[i.e., in my home hierarchy, with its parent folder always being renamed to indicate the current version number inside]
When i first tried the MAS, i grabbed the (TextWrangler) version 3.5 update. To my surprise, the app downloaded right in place to the same path above, despite the "3.1" in the parent folder's name (which i subsequently changed to 3.5).
