RepSwap changes your tracked reputation based on the last faction you earned reputation with. It is very lightweight and requires no configuration from the end user (you). RepSwap was created for a guildie who was rep grinding one night and wouldn't stop complaining about having to change her reps around every time she wanted to watch a new faction.
All Stable Releases of RepSwap are automagically packaged on Curse and available through the Curse Client. The addon can be downloaded from the RepSwap Project Page using the manual function or the client buttons.
If you are interested in contributing to the addon or just want to check out the code feel free to check out the RepSwap Source Code on Github.
I ask that all problems with the addon are reported to the RepSwap Issue Tracker on Github. Checking the Curse project page can be a bit of a pain in the ass sometimes and it helps me if I can keep everything organized in one place.
Thanks for checking it out and I hope someone else can make use of this addon!