I am working on a model and the only unwelded vert is inside the top of the mouth. I got to level 3 and then i noticed....probably a couple hours worth of work. Is there anyway I can export and re import as a layer after I weld the vert and have all my sub-d levels still there? thanks.

Does your model have UVs?  If so, you could import as layer based on UVs instead of vertex IDs (because welding that vert is going to change your vert order).

Yup...tried that, no UVS were set up, so that is not an option either.....I guess next time I should be more careful and learn from my mistake. Thanks for your help though. More practice can’t be that bad.:)

Well, all isn’t totally lost.  One thing you could do is:
1) export out lvl 0
2) in Maya/Max/whatever, weld the vert then UV the model
3) bring back in to Mudbox along with existing lvl3
4) bake a displacement map to new lvl 0 with UVs
5) apply the displace to new lvl 0 - now you should have your original sculpt on the new base model with the welded vert and Uvs

Might require a little cleanup, but could save a lot of rework - not sure how far along you were.

Well, all isn’t totally lost.  One thing you could do is:
1) export out lvl 0
2) in Maya/Max/whatever, weld the vert then UV the model
3) bring back in to Mudbox along with existing lvl3
4) bake a displacement map to new lvl 0 with UVs
5) apply the displace to new lvl 0 - now you should have your original sculpt on the new base model with the welded vert and Uvs

Might require a little cleanup, but could save a lot of rework - not sure how far along you were.

This will definitely work, I’ve done this before. Just make sure the points that need welding are as close to each other as you can get them in the high-res model In your case since the open vert is in the mouth cavity, clean-up will be very easy.

Thanks for the replies! I may try that....if I run into any trouble I will probably be back here asking questions again. Very much appreciated!:)