replace last instance of a character only if...

[wfejessie]

Is it possible to replace the last instance of a character? And if it is, is it possible to replace it only if the file name ends in a hyphen & number? Example:
CER-1234
CER-1234-G
CER-1234-WG
CER-1234-1
CER-1234-G-1
CER-1234-WG-1
The first 3 should not be changed. On the last 3, the -1 should be changed to _1.

[Luuk]

With RegEx(1), the "Match" and "Replace" can be like...
(.+)-(\d)$
\1_\2

[Admin]

Aos, with the Javascript renaming you could write a Javascript routine that can get as complex as needed.