Is an PDF-X1A still a PDF-X1A after using "Reduce File Size?"

Let's say you create a PDF-X1A (PDF/X-1a:2001), and the file size is very high. Will using "Reduce File Size" degrade the X1A to the point where it no longer fits the X1A criteria? There's a debate here as to if "Reduce File Size" just eliminates extraneous info, or if it actually degrades the file to the point where it's not X1A compatible anymore... Is there a way to reduce the size of an X1A so it's still worthy of the X1A criteria?

Thank you!