Slide Partition from Rowstore to Columnstore
No, this is not possible. ALTER TABLE... SWITCH is a metadata operation and both tables need to have identical schemas. There's no such thing as a partitioned table that has some columnstore partitions and some rowstore partitions.

The best you can do is switch the rowstore partition out, build a clustered columnstore index on the switched out table, and then switch that table into the columnstore table.