Not really. It's pretty simple to do.
The only step I occasionally find a bit fiddly is refitting the downshift button and it's return spring, but even that might only take a couple of tries to get right.
You can't really tell visually if the springs are worn, so I always replace them anyway on shifters I get from eBay.
The cracked carrier is obvious - it's usually the post that snaps.
Note that I have only ever had to replace the right lever parts. I have yet to find a left shifter that is sufficiently worn to lose its click.
A 4-pack of springs and a 5 pack of carriers will cost you around 20 quid. There's a seller on Amazon called Y frame discounts that usually sells them at the best price Inc postage. Places like GB Cycles will sell you them individually if you want to do it that way.
The part numbers you need are EC-RE209 & EC-RE211.
I buy mine in bulk now as I've decided I want my 10 speed fleet to last forever lol.