Hi all,
I have some string data where this '17081234_235_236' means '17081234', '17081235', '17081236'. More generally, I need to go from this kind of input:

to this output:

Note that the length of the '_' extensions can vary, and if the length equals or surpasses that of the original string then the operation is merely split-to-lines, i.e. no in-filling (lines 4 and 5 of the input example).
Any ideas for an elegant way to do this? -thanks, Mikael