I don't know any "render and replace" function in premiere. If you are referring to "replace footage", I dont see the point why that shouldn't work. As far as I know you can replace any clip already in the timelines with any other clip regardless of file extension or codec. Generally speaking I doubt that any editing software is happy about changing a framerate of the source clips though, so I would strongly avoid that. Also I don't see the point... Whatever you are doing in virtualdub, why can't you export it with the same fps?

I don't know any "render and replace" function in premiere. If you are referring to "replace clip", I dont see the point why that shouldn't work. As far as I know you can replace any clip already in the timelines with any other clip regardless of file extension or codec. Generally speaking I doubt that any editing software is happy about changing a framerate of the source clips though, so I would strongly avoid that. Also I don't see the point... Whatever you are doing in virtualdub, why can't you export it with the same fps?