I have a couple of packages (luaotfload being one of them) for which I make use of the bleeding edge development version which has not been uploaded to CTAN yet. Now, this version can live quite nicely in my user texmf tree, but when placed there the flavor of TeX being used (LuaTex for this particular package, but the question is not specific to that flavor) will always find that bleeding edge version first and use it. On occasion, however, I have a document for which I want to go back to the stable version which is available on CTAN (and thus in my TeXLive managed texmf tree). Is there a way to tell the TeX engine not to look in the user texmf tree when looking for a particular package (I cannot simply skip the user texmf tree for all packages as I have some personal ones there which I use in nearly ever document)?
Alternatively, if I were to setup an "experimental" texmf tree (and place the bleeding edge package there) is there a way to instruct the TeX engine to look in that tree before looking in the usual places? Bonus points for a solution that can be controlled on a package by package basis, though I'm usually either using all the latest stuff, or only CTAN released stuff with a particular file.