MERGE and UNMERGE cells quickly

I have a file with at least 500 rows that contains merged cells down the columns. but as you know - it is impossible to properly sort or filter columns having merged cells. how can I quickly Mere unmerge cells down a column going from ABC to EFG and vice versa. I would like to be able to changes column B to look like F and vice versa quickly. (the content would stay where it is at in columns ABC and not actually move to EFG.) Thanks in advance