How about using a flip-flop operator? 
while (<DATA>) {
  /# input for/ .. s/1\.00/5/g;
  print;
}
__DATA__
# input for Data

1.00  0.99  0.92
1.00 -0.22  0.61

[download]
or, to avoid warnings about "useless" use of flop, 
use strict;
use warnings;
while (<DATA>) {
  if (/# input for/ .. /\d/) { s/1\.00/5/g }
  print;
}
__DATA__
# input for Data

1.00  0.99  0.92
1.00 -0.22  0.61

[download]
The PerlMonk tr/// Advocate

In reply to Re: Edit variables in file by Roy Johnson
in thread Edit varaibles in file by indie_campbell

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