import re
my_string = "T-46-5-В,Г,6-В,Г"
my_pattern = r"^(\D-\d{1,2}-)[\d,]+(-[а-яёА-ЯЁ,]+,)[\d,]+(-[а-яёА-ЯЁ,]+)$"
new_string_parts = ["005", "006"]
new_string = re.sub(my_pattern, fr"\g<1>{new_string_parts[0]}\g<2>{new_string_parts[1]}\3", my_string)
print(new_string)
# => T-46-005-В,Г,006-В,Г
aW1wb3J0IHJlCgpteV9zdHJpbmcgPSAiVC00Ni01LdCSLNCTLDYt0JIs0JMiCm15X3BhdHRlcm4gPSByIl4oXEQtXGR7MSwyfS0pW1xkLF0rKC1b0LAt0Y/RkdCQLdCv0IEsXSssKVtcZCxdKygtW9CwLdGP0ZHQkC3Qr9CBLF0rKSQiCgpuZXdfc3RyaW5nX3BhcnRzID0gWyIwMDUiLCAiMDA2Il0KbmV3X3N0cmluZyA9IHJlLnN1YihteV9wYXR0ZXJuLCBmciJcZzwxPntuZXdfc3RyaW5nX3BhcnRzWzBdfVxnPDI+e25ld19zdHJpbmdfcGFydHNbMV19XDMiLCBteV9zdHJpbmcpCnByaW50KG5ld19zdHJpbmcpCiMgPT4gICBULTQ2LTAwNS3QkizQkywwMDYt0JIs0JMg