1. Backup itemkinds1.txt, it's in Modules/cRPG.
2. Open it, using notepad CTRL F look for arrow_flying and bolts_flying. It will
be in quite a few different combinations with specific arrow models etc. - it
doesnt matter.
3. Replace every phrase containing arrow_flying and bolts_flying with flying_missile.
So, if you have
"tatar_arrow_flying_h1" you change it to "flying missile"
"steel_bolts_flying_h1" you change it to "flying missile"
etc.
4. You must do it for every occurrence of the mentioned phrase.
5. Save the file!