how to add a new tile sheet, having trouble with adding new tiles to the engine, Want the answers then please read Xeylas post 2 Options

[NocturnalDim]

I was wandering how could i Insert a few ground/roof sprites without messing up my maps that i've already created?
What happens is when i insert a new sprite sheet it removes my already existing material turning my maps in pure trash (water becomes rock, trees become stools, etc.) how do fix that?
Even better how can i feel up empty "E" section with the stuff i want?