XSLT 1.0 provides a fairly limited range of operators for string manipulation: concat(), substring(), substring-before(), and a few others. But you can do surprisingly complex things if you learn how to write recursive templates. XSLT 2.0 has a much richer repertoire including full regular expressions - matches(), tokenize(), and replace().
If you have a specific problem achieving a specific transformation with these functions then I can help you. However, you must first specify the problem precisely, and you then need to make your best efforts to solve it for yourself. I'm not going to write the code for you.
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference