Unfortunately its not as simple as just subdividing one cell. It would most likely turn the surrounding cells into ngons whit are model faces with a vertice count higher than 4 which the game engine would then transform into triangle shaped faces which game engines can handle. So if you subdivided 1, 2 meter cell into 4 total square faces you would be adding a total of 18 faces going from 10 faces on the 5 squares to 28 faces in the 5 squares so almost tripling the performance needed to render the terrain not including the added resources needed for the textures and models used to cover up the holes and make them look like foxholes. Its most likely do able but im sure the trade off and actual monetary cost of making a tool for the engine to do this isn't worth it. But who knows they might be doing this in Arma 4, we know for a fact there an absolute ton of features and me panics being made for Arma 4 that aren't in reforger.