Would it be easier to just decompile the map? You'll lose texture coordinates, but I suppose it's not too hard to do those over again, particularly if you're going to retexture them anyway. Note: There may be copyright issues depending on who's map you're trying to modify.

Why are you so in need of doing it without a recompile? Maybe the underlying problem can be solved much easier.

If vis is taking that long, you're doing it wrong. You need to learn to use detail brushes to simplify the BSP. Typical maps should compile vis in minutes.

If vis is taking that long, you're doing it wrong. You need to learn to use detail brushes to simplify the BSP. Typical maps should compile vis in minutes.

I knew I forgot something in the process, but wasn't sure what it was. Thanks for that.

For conventional space maps you can just convert all the geometry inside the skyboxes to detail.

If the geometry doesn't help to seal the map or divide up the portalling efficiently then it should be detailed.

I really don't think those 196 units matter. Also, you're saying the skybox brushes were 256 units away from the center? I really doubt that, as 256 units sounds like the width of a generic corridor. Do you have your units and "little grid squares in GtkRadiant" mixed up?

Ok genius, can you explain to me why it would matter? What is the technical reasoning behind it mattering? Because I really don't believe it does.

The VIS stage takes the whole map from center of grid (0 0 0) There start 4 initial blocks. While the center of map is 200-300 units away from the center, the VIS calculation causes problems, because the initial blocks splits the map 200-300 units away from center of map. As the map is centered into grid, there are blocks symmetricaly splitting the map. Then it's easier to calculate VIS.
If I've messed some, let's correct me...