2 things to be aware of before you do try this (this isn't for metl who already knows this...):
Firstly, lightmaps are loaded into a "blocklights" array before being sent to OpenGL. This is hard-coded to a size of 18*18, and is dependent on the max surface extents. If you boost the lightmap density you will need an engine modification to either reduce the max surface extents or increase the size of blocklights, otherwise you'll risk overflowing the array.
Secondly, you can expect dynamic light modification to be a serious performance hit.