Suppose a company already has an ISO 9001 certification. Then they decide to achieve an appraisal at level 3. Suppose further that their plan is to add additional process assets according to their gap analysis. But then they discover that certain ISO 9001 work instructions or templates require changes to meet the requirements of CMMI level 3. If these assets are changed, would that necessarily invalidate the ISO 9001 certification? Under what conditions would the certification be invalidated, and what needs to be done under those circumstances? Is there a way to avoid this issue?
Without having any details as to your situation, I find it hard to believe that if you are ISO 9001 certified that the CMMI is causing you to make changes to your quality system that would invalidate your ISO 9001 certification. The ISO 9001 standard and the CMMI-DEV model are compatible. Are you working with an SEI-certified Lead Appraiser/consultant? If not, you may be making some decisions to change processes and process assets that are not necessary.
To properly address your concerns, you should have a Lead Appraiser conduct a gap analysis of your organization to determine what you currently have in place that is compatible with the CMMI and identify those gaps that need to be addressed in order for your organization to achieve Maturity Level 3. And any updates to existing processes and process assets should be compatible with both the ISO standard and the CMMI-DEV.