I was mucking around with Oasis' "Don't look back in anger" on the acoustic guitar/vocals.
I was using these chords, but on capo 4 as I reworked the song a bit: http://tabs.ultimate-guitar.com/tabs/o/oasis/dont_look_back_in_anger_acoustic_ver2_crd.htm
For fun, I tried substituting all the chords with their relative major/minor versions e.g. C<-->Am, G<-->Em, F<-->Dm (wasn't sure what to do with E7). It sounded pretty cool.
I wondered if this is something that has a name... what am I actually doing from a music theory perspective? Or, am I just writing a completely new song?