which basically leaves the 'map it yourself' process. It would be nice if HL used the same engine because they have some neat maps, but looks like the only available way is to map it yourself
.:c|H|EE|TO|H|s|:.
Need a thorough map tester? Shine the Cheetohs signal!
Yes you can, but HL maps are way too small and the scale is wrong. Plus, the decompiler generates thousands of useless brushes you have to repair, the textures must all be redone and all the entities must be replaced. When you are all done, you'll have spent several hundred hours and have a small crude map by MOHAA standards.
rouge plugins help with the duplicate planes. the textures arent really that hard to convert, it is small though, your are right, but ti wouldnt take hundreds of hours.