I want to identify and replace the third occurrence of the "T" character in each data row
AGCTTAGGCGAGTGCGAGTGCGATA
AGCTAGGCCGTAAAGCGAGGAGCCC
CTAGCATGCATGGGACCTAGGACCA
TAGAGATCGACGATTTACGAGGTTC
to
AGCTTAGGCGAGUGCGAGTGCGATA replaces it at character 12 (base 0)
AGCTAGGCCGTAAAGCGAGGAGCCC only 2 occurrences, replaces nothing
CTAGCATGCAUGGGACCTAGGACCA replaces it at character 10
TAGAGATCGACGAUTTACGAGGTTC replaces it at character 13
This is a simple case. I'm looking for something like this that will work for any occurrence and any character or string more generally. I expect it will require REGEX, but I'm not yet proficient with it.
