Why not extended the PROP we got
Click with PROP = edit
Shift + drag and ctrl + drag = rectangle/line edit (Like which in your mod)
Shift + ctrl + drag = normal drawing I think? Because PROP edit already do the 'flood fill'
Or, click with PROP = draw
Shift + drag and ctrl + drag = rectangle/line edit
Shift + ctrl + drag = flood fill edit(What the PROP now did)
OMG finally! Never again will you have to tediously change the property of each individual pixel.
Anyways, I think it should highlight or outline what's to be edited in some way so that you dont have a cluster of pixels escape your attention and cause confusion later.