Thank you so much for your help

You're welcome.

If I understand your script correctly, you are setting the line delimiter to a ";"

Yes.

and replacing all multiple spaces to single spaces?

\s refers to all types of whitespace; refer to perlre. The key here is that \s includes the newline character (\n). So, \s+ replaces multiple adjacent spaces, tabs and newlines. s///g changes all whitespace on a line.

For older netlists with ~5k cells, the script takes about 12 hours.

That is a surprisingly long time. Can you post your code for that?