How to enter multiple Affected Objects in an ECR

Yes, copy/paste. Open up a search in a new tab. Find the items you want and select what you want to add to the affect object section. Click copy. Go over to the affected objects page in the CR (assuming you have the edit popup open). Click paste.

Other than copy/paste method, I also use a semi-colon as a delimiter when searching for affected objects.

PartA;PartB;PartC;etc.  There is a string limit, so you may need to execute more than one search.