Why do my dwellers change outfits during exploration? Can I change it back to what I sent them out with while they are still exploring?
In case they find a higher tier outfit they'll swap it. And no there is no such way as far as I know.
This frustrated me times ago aswell, when I had an dweller wearing an +3 strength outfit to get him with all stats maxed into the wastelands and he found a rare outfit and changed to it while the new one he was wearing was even making him weaker.
Sadly this is one of the things they solved in an inlogical way.