Regex: \10 vs $10

You can only use up to 9 capture groups with the normal regexp mode.

If you need more you can use VBScript's regexps instead (see here) assuming they allow it. I haven't tried but VBScript uses the $1 $2 etc. syntax instead of the \1 \2 etc. one, and it seems that regexp engines which use $1 tend to allow $10 while ones which use \1 would interpret \10 as \1 followed by a 0.

(Of course, if you are calling into a rename script then you then have other tools at your disposal which might make more sense than using regular expressions at all. That's up to you.)

Having said all that, if you look at your example, you don't actually need 10 capture groups in the first place. Some of them are right next to each other in both the input and the output, so you could combine them into a single group. You only need to start a new group if you want to remove some characters before that group, or insert the group into the output in a different place. Generally, if you need more than 9 capture groups then there is probably something wrong with the approach or something has been made more complex than it really is.