how do i replace item in hand with new item and in the same hotbars

Couldn't you just make the tazer not have durability?

I'm not sure I understand what you mean.

You want to create a tazer with two modes of fire ? is it this ?

And for the durability, i don't now but possibly 0 durability make a invincible tazer.

Otherwise you can create a item an say in the procedure :

When right-click

shot with the ranged weapon [tazer]

If you use this you have to create a ranged weapon [tazer] unavailable in survival

I've write below a tips to create your invincible tazer with 2 fire mods :

create 2 ranged weapons : [tazer1] and [tazer2] unavailable in survival, create 1 item [tazer item] available in survival and 1 item [tazer2 item] unavailable in survival.

Say for the item [tazer item] :

When click in air

Shot with the ranged weapon [tazer]

___________________________________

When click on a block

remove [tazer item] from player inventory

add [tazer2 item] to the player inventory

Say for the item [tazer2 item] :

When click in air

Shot with the ranged weapon [tazer2]

___________________________________

When click on a block

remove [tazer2 item] from player inventory

add [tazer item] to player inventory

I hope I have answer your question