Super easy. You'll have a new seam at the center back of your waistband, but your pants will stay up. If you have to take the waist in more than a couple inches, it's your ass and not you thighs and don't bother trying to take the waist in at the side seams anyway. This is also the place to take your pants in if the back end is a little baggy. Or if you just want a little more definition.
You can probably eek out an extra quarter to half an inch at the center back if you need to make the waistband bigger. You can also reposition the button above your fly, but only if you have a button. Rivets and hooks are punched through the fabric and don't reposition well. You'll be able to get the same quarter to half an inch if you're just too bootyliscious for your pants.
Something you might be really excited about the possibility of altering even though you had no idea it was even possible. Okay, it's only sometimes possible. HRD wouldn't do this on jeans and you risk fussing with your pockets and zipper. But if your waistband is continually too high or sitting right on your belly button piercing, you can see if your tailor will shorten the rise. If it's the for your belly button piercing, just shortening the rise in the front will do just fine. HRD wouldn't recommend shortening the rise in the back, unless you're lacking boobs and just need to show off some sort of cleavage. Unfortunately, you can only lengthen your rise in the back a half inch at best. The rise can only be lengthened a half inch at best everywhere else.
The between the legs interlude: super tricky. Crotches are tricky enough to draft in the first place with people wanting a slim fit with just a little cupping of the ass but no possibility of indecent exposure.
If it's a little baggy, or if you just don't have enough swag for how baggy your pants are, just hike them up a bit. Wear them with a pair of suspenders. HRD counts this as an excellent fix as not only do your pants look better, but it was cheap, quick, easy, and it got you into suspenders (just wait until HRD writes all about how suspenders actually literally hold your pants up while belts just cinch them around your torso and hope). If you and your pants are looking good like this, you can make the change permanent by taking in the waistband or shortening the rise (make friends with your tailor).
Even though the solution to a too tight crotch isn't suspenders, it's pretty easy too. Your tailor should be able to sew a new, lower seam and trim the excess. You won't need to lower the crotch much to feel the difference. Just half an inch can give you loads more room.