No, it's not difficult. If you look in the Studebaker Shop Manual, they show the guides being driven out and in by hand with a BFH. These days, I use an air hammer do drive them out and in. Whichever method, it's a must to have a piloted driver which closely matches the ID and OD of the guide.
Maybe, however you get the guides out and in, the key to a good valve job is someone who knows how to hone the guide to the proper ID.
Bottom line, getting the guides driven in is the easiest part of the job.