If your numbers after #do not have spaces after them, you can use:
:g/\([0-9]\+\) /s//\1.0 /g
Using ()creates groups that you can name \Din the replacement text, where Dis the position of the group in the search bar. This will give you:
1.0 1.0 0.0 # 1
6.0 1.0 0.0 # 2
8.0 1.0 0.0 # 3
10.0 1.0 0.0 # 4
12.0 1.0 0.0 # 6
If they have spaces after them (which looks like you have), you will get:
1.0 1.0 0.0 # 1.0
6.0 1.0 0.0 # 2.0
8.0 1.0 0.0 # 3.0
10.0 1.0 0.0 # 4.0
12.0 1.0 0.0 # 6.0
in this case you can:
:g/\.0\( *\)$/s//\1/g
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