What follows if the 4.7-inch modification works?

Could the four-inch guns be removed at the first refit once the dual-purpose 4.7-inch mounting proved itself?

Yes. The same proven modification could also let Tribal, L, and M-class destroyers retain 4.7-inch guns in positions otherwise fitted with four-inch weapons.

The first refit could remove the four-inch battery once the modified 4.7-inch mounts had proved their performance. The larger consequence would be a tested conversion available for destroyers. A Tribal might retain a dual-purpose 4.7-inch X mounting instead of replacing it with four-inch guns. L, M, and other destroyer classes could follow the same path, provided the modification had already been developed and demonstrated.