If you really just want to change the plates then as Slob says the basket wear will need to be re-dressed and to do that properly you will need to take it out anyway so you might as well change it for a new one and be done with it.
How many miles has it done?
Mine had done 30k when I changed it but I did re-dress the basket and plate tangs a couple of times but if you were to go by the factory measurement for the basket to tang gap you'd be changing them every year- the friction material was still in spec though!
Comparison of old and new baskets:
I wouldn't use one of those 'bolt to the engine' holding tools though- there's quite a lot of force when both un-doing and re-torqueing and likely something will give and at best will result in skinned knuckles.
I bought a holding tool from a chap making and selling them on eBay- about £25 posted, combined with a cheapo impact gun still made it cheaper to do myself than putting into a shop- plus I got an impact gun and we all need new tools right?
