I was going to convert the Wool Trenchcoat from the Mother Russia set from the store for females (planning to do more so we can have some masculine clothing for AFAB sims), but upon trying to export any of the GEOM files, i get an error message [attached below]. I don't know what to do. And when I export in bulk, which is the only time it lets me, i try opening up the geoms one by one in blender and none of them work [also attached]. What am I supposed to do/what am i doing wrong?

I believe you have to decrapify store content before you can make any changes. The tool and a tutorial can be found at More Awesome Than You forums.