There used to be a guy here who was a Catholic convert to Mormonism. He said he received communion, while remaining Mormon. I don’t think a Priest would view that favorably, but he never checked in with a Priest. Just doing his own thing. Like I said, some Mormons have this thing about building a personal syncretic religion. I sometimes think they have a view of themselves as mini Joseph Smiths.
I live in Utah, so General Conference is reported in the local news. I’ve seen the invitations to come back. I think that would only be appealing to someone who still maintained a belief in the foundational claims of Joseph Smith. I think the LDS Church believes that people who have left still believe, just have problems with this or that, and they’d rather keep them around than drive them off.
There are many of us, hundreds every year in RCIA in Utah, who do not believe Smith was anything but a conman. Every person is different. Some have a difficult transition to Catholicism, for various reasons. Others, transition so smoothly you’d never know they were ever LDS. All, just show up, no Catholic is out there proselytizing Mormons, door to door. I think if we did, we could effect a mass conversion.