rom editing

[Guest add.thebad]

Hi

I have been using android for and am happy flashing and changing roms but i now want to start editing roms and making them more to my taste

Im i right in saying i can do this

Download a current rom

unpack system.img with unyaffs

change apk's and frameworks inside their

then how do i rebuild system image?

and can i then just do a nanroid recovery on that?