Valve Stem seals / replaced while still on the motor???

[Peter]

I was wondering if it is possible to change out the valve stem seals while the head is still on the block...I am to change out my lifters and thought I could go a little further

[Master ACiD]

i suppose you could. just do 1 cylinder at a time and make sure that the cylinder youre working on is at top dead centre so the valves dont fall down into the engine.