this will require the console and element viewer, be careful as messing with both of these too much has the ability to ruin a session so follow this very closely

finish your first shot, and then make your second

NOTE this may cause the exported audio to lag, so its advised you readd audio in post if you choose to do this.

go to the element viewer and press this (if you had previously used it for something) to go up until you see session

your screen should look something like this

press the plus next to activeClip, find mapname, and completely remove the text from the box adjacent to it.

then find subClipTrackGroup and click THAT plus, then click the plus next to tracks, then the plus next to the green text saying Film, and finally the plus next to children

then under any shot, click the plus and look for "mapname"(the one under shot, not the one you previously cleared), and change the map to any map of your choosing,

afterwards, go to the console and type "changelevel (mapname WITHOUT .bsp)" example being changelevel black_void, this will make sfm load the black void map and allows you to freely animate and do things in said map (if the animationset editor isnt showing any new models, move the playhead to the previous shot then back to the current one),

though, you may notice that your previous shots say" WRONG MAP LOADED", dont worry about this, as if you want to go back and edit the shot, you can simply type "changelevel (map that shot was in)" and freely edit, don't worry about rendering, as sfm will automatically load the map when you render your animations

if this doesnt work tell me because im doing this solely from memory and i might have missed some details that i just have muscle memory doing