How often to sevice suspension forks Consider a SunTour XCR coil fork or any similar. Service manuals suggest "full service" every 30 hours of riding time.

I take that to mean removing the boots and re-lubing the stanchions. 

However, this includes the removal of the grips, in order to remove the hydraulic front brake lever. I am worried that the grips are being worn out by this process, causing them to turn freely and thus be very inconvinient for rideing.

In this situation, how often should I service the fork?
I think 30 hours is probably conservative, it's too often and won't add much additional value. That would be about right for an air sprung fork with an oil damper, possibly even a coil with an oil damper, both in dusty conditions.

Fork service interval for each fork is dependent on the fork, the type of riding you're doing and cleaning you do after each ride. Servicing is done to ensure optimal performance, prevent accelerated wear and prevent failure. Generally servicing of forks includes a replacement of oil and seals, a thorough clean (to remove grit) and a lubrication. 

Suntour coil forks use a sealed unit for damping and the coil spring. This means there is actually very little servicing the can and should be done. Apart from the dust seals I don't think there are any seals inside the fork to replace, so pulling it apart would only be to clean out any grit that had got past the dust wipers/seals. Servicing would be pretty simple once the fork was apart clean the dust seals, degrease anything that had dirt contamination, re-grease and check the elastomers to make sure they aren't deteriorating. 

In terms of removing the fork, if you have a repair stand you could remove the brake caliper and drop the lowers off. I imagine you have the XCR RLO and the remote is why you need to remove the grips, apart from lock on grips or split clamps there's no easy way sorry. I've always found grips give out pretty quick anyway and start sliding around so now stick only to lock ins.