I get the 'light-finger' syndrome at times myself <g>

For the copying process there's not much cure except extra care.  For doing
the same type of thing when you're formatting a separated bunch of cells, I
find it safest (even at the cost of a little convenience) to select a bunch,
do the format, select another bunch, repeat...  Nothing like having selected
about a zillion cells and just when you get ready to select the very last
one, having your finger get tired, become slippery or suddenly lose weight!  
[Murphey rules - and he was an optimist]