Note: Used translator for the text below because I could not find a good way to explain it in English myself.
I think it could be even better.
All missions and vehicles have a fixed ID number. Since this will never change, you could also consider a system that uses it.
Name the files after the ID of the object (with a small adjustment the ID can also just be visible in the list, so you can easily see which mission is what). For example: You have an icon for a forest fire with the ID 101. You name that icon 101.png, then you go to the uploaded one and there you can select and upload all files at once. The system reads the IDs and links them to the missions. The same for the vehicles.
To distinguish between green / yellow / red missions and the different animates for the vehicles you can use an additional tag like "101G.png / 101Y.png 101R.png" and the same for vehicles.
Because you have 1 single uploader, you can select and upload everything at once, the system ensures that the correct IDs are read. You can also upload 1 single file via the same system if you only want to adjust 1.