I would probably stick to the solutions already suggested with the concatenation operator, but you could also use zero-width positive look-behind and look-ahead assertions to check whether the tags are there around your 11-digit number, but not consume them in your substitution. Something like (?<= pattern) and (?= pattern), with pattern describing your start and end tags.

In reply to Re: Regex substitute with both a sub and other data by Laurent_R
in thread Regex substitute with both a sub and other data by FloydATC

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