Here a minimal demo in the debugger to highlight your problems.

  DB<8> $_= "parameter=TO_DATE('1900-01-01','YYYY-MM-DD')\n"

  DB<9> s/=/="/

  DB<10> s/\n/"\n/

  DB<11> p $_
parameter="TO_DATE('1900-01-01','YYYY-MM-DD')"

  DB<12>
[download]

But I'd rather suggest using split /=/ and join on individual lines, using your regexes on a complete file will cause havoc if the RHS contains any '='.