series_flagger.mip is the file you will want to edit and drop into your "objs" folder to change the flagger and official.
You can expand the objs.dat in the objs folder to find the "series_flagger.mip" file. Then use something to convert it to a bmp or tga to edit with a paint program.
You can use a pit crew template to edit the uniform, if you can't find a series flagger template.
Search for a "series flagger" template and you might have some luck finding one that works and is not a dead link.
When done, save and convert it to the mip, slap it into the 'objs' folder and see how it looks.
Have fun!