Short answer

1. Yes, I think the best way to do that is with line input, i can't think of a simpler way (except just copying the data or putting the data in an external file)
2. You have swap all map positions on the level you want to delete, up to the last level. You might want to delete the data (replace the data with 0's) later or before that. you can swap 2 levels by swapping all locations of the levels
(SWAP var1, var2) for all the array locations on that level
So:
'swap level1 and level2
for x = 1 to 800
swap map(level1, x), map(level2, x)
next

and you have to do that for the level and the level above it, then for that level and the level above it, and so on, until you have reached other empty levels...
I hope this was a bit understandable :P