If the file below 0f 239 records is processed by the code below it throws no errors and writes the output...but the output has 615 records instead of 239 seemingly having written any revised ones three times instead of only once.

replacements = {'/1':'/01', '9/':'09/', '7/':'07/'}
file2 = open(r"c:\users\liddvdp\desktop\IBC CAP OUT.txt", "w")
with open(r"c:\users\liddvdp\desktop\IBC CAP.txt", "r") as reader:
         for line in reader:
             for src, target in replacements.items():
                 line = line.replace(src, target)
                 file2.write(line)

That's because you're writing an output line once per replacement rather than once per input line.

For usage questions such as this, you'll be better off on a forum such as discuss.python.org, the python-list@python.org mailing list, or the Python Discord community (pythondiscord.com).