When you send out a notice 30 days before a change is in effect, is it required to bold the changes?

You must draw attention to the changes some how. This doesn't have to be bold print. It could be a letter explaining the changes.

Refer to the Commentary to 230.5(a)(1):
1. Form of notice. Institutions may provide a change-in-term notice on or with a periodic statement or in another mailing. If an institution provides notice through revised account disclosures, the changed term must be highlighted in some manner. For example, institutions may note that a particular fee has been changed (also specifying the new amount) or use an accompanying letter that refers to the changed term.