Would the Reserve HR Specialist role vary between different units. E.g A Medical unit compared to a Artillery unit etc?

Hello thanks for your question.
To be honest I can only speak from my experience as a regular soldier as a HR Specialist but I assume it will be similar to the Reserve role.
The role itself doesn't necessarily change between the different units you are attached to but your daily work schedule might. What I mean by this is some units do things differently so when I was attached to the Royal Engineers, they would involve me with their exercises and I would do PT with them and I even managed to be involved in with engineering tasks such as Bridging. Other units may not involve you as much. Your clerical work shouldn't change too much but units may want their administration done differently so you may found yourself creating different reports or running certain checks differently. The core role should remain the same.
I'm sorry I cannot answer from the Reserve side but I hope I've answered your question as much as possible?
Zoe