Upon right clicking a guard villager, regardless of whether "giveGuardStuffHOTV" is true or false, the window to give guard villagers gear will not display, thus the guard villager will not e able to have their inventory modified by the player.

I've not observed the same - I've been able to give a villager a sword with shift-right click, then right click the guard to open the UI. Can you try again on a new world with just Guard Villagers installed? It might be another mod interfering. Could you also let the mod author know which version of minecraft and the Guard Villager mod you're using?

I was able to give them swords/crossbows only after I got Hero of the Village

yes i have the same problem on my server , no matter these setting
"giveGuardStuffHOTV": false,
"setGuardPatrolHotv": false,
"ConvertVillagerIfHaveHOTV": false,

u just cant give them anything or interact with them.
which sucks cause patrols and raids are off at the server