Your description suggests you're creating multi-level lists, for which you should be using Word's multi-level list numbering tools and properly-defined paragraph Styles to associate with them. With that approach, your paragraphs can be numbered automatically (parentheses included) and, should you need to insert/delete/promote/demote one, all the numbering will auto-adjust.

If you're wedded to your present approach, you could use some wildcard Find/Replace expressions to apply the parentheses. For example:
Find = ([a-z])([0-9])([A-Z])([0-9])
Replace = (\1)(\2)(\3)(\4)
would changed any string like a3B1 to (a)(3)(B)(1) - throughout your document or for just a selected range. No macros required.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]