I just want to make sure I am thinking correctly. The plan I am working on does not currently have a match feature in the document. Can we distribute a SMM and start the match contribution a week later or is there a waiting period??

Also, if the plan has prior year testing can we rely on the 3% for NHCE ACP discrimination testing or do we have to change to current year testing?

there is nothing I know of to prevent you from adding a match, and since that option wasn't available then you can use the 3% prior year for testing. you would need to decide of course whether this would be done on a payroll basis, etc