Depends on your existing Regex.
For example:
^\d+$
Would allow only numbers.
^[-+]?\d+(\.\d+)?$
Would allow numbers with a decimal point, and an optional leading plus or minus.
To allow or disallow specific characters, we'd need to know what you want to permit - but get a copy of
Expresso[
^] - it's free, and it examines and generates Regular expressions.
It'll help you design your own to fit your specific needs.