As per Who places the anchors that rock climbers use? it seems that there usually isn't a legally established authority managing rock climbing routes. As such, its up to groups of volunteers to maintain and establish new routes. Given this fact, can anyone just go ahead and create their own routes? I.e. can you take a drill, choose a random slab of rock next to an established climbing spot, and add a bunch of bolts for a new route?
Yes and no. Of course anyone can go and drill a hole in some rock, but without the land owner’s permission you risk getting into trouble, possibly even prosecution for criminal damage or, if where you are bolting is a nature reserve, wildlife related crimes.
You also risk the ire of the local climbing community if you bolt a route that is considered a trad route, and in fact this happens from time-to-time and those routes are then de-bolted.
In the UK, the BMC (British Mountaineering Council) will often publish local policies on where it is and isn’t OK to bolt routes (as a rule of thumb, it’s OK to bolt quarried rock, but not unquarried rock - but there is a strong trad ethos in the UK, less so in Europe). The local BMC polices are unenforceable, but it would behoove people to follow them. Also, the BMC often negotiate access rights to private land for climbers, and in those negotiations there will be agreement with the land owner over what they are happy to be bolted and what they are not. Other times, a land-owner might simply turn a blind eye to the bolting, or remove the bolts themselves.
Locally, I know of several places where someone has put in bolts at the top of a training face, mostly so that people using the face can be belayed from the bottom. The face is about a quarter mile long and 60 to 100 feet high. As far as I know, the local mountaineering association doesn't care about this type of situation.
The jursidiction is provincial forest, in a region designated recreation area -- not enough access to wood to make it economical to log.
(The location is near Windy Point on Lake Abraham, about half an hour SW of Nordegg, Alberta, Canada)
So, yes: Depends on local rules and customs.
Practically: You could get away with it on any region that is not part of a noteworthy climb.
Getting away with it one thing. When should you do it?
If the route is suffering from overuse, and the impact of using bolts is preferable to having bongs, chocks and pitons constantly added and removed.
If the rock doesn't accept normal climbing gear. I have seen rock that seemed to need an ice screw rather than a piton. Or a 6" x 3/8" hole, a big zinc insert anchor and a lag screw. There may be merit in setting an anchor with epoxy cement. Or ordinary cement to make a route more commonly usable or safer to use.
A location used primarily for training.
When should you not put in permanent anchors:
If you're a newbie. Wait until you are much more experienced. Some things you think need a permanent anchor now, you will free climb in 5 years.
If there are esthetic reasons to not place them. They are ugly.
If it would restrict a broad face to a single route.
If it turns a really difficult, but feasible route into one that is boring or routine.
If would prevent the thrill of discovery, of finding your own way.
This latter one is why I no longer circulate logs of hikes and canoe trips I've done. Part of my enjoyment is the feeling of being the first, or being the first one in a lonnnnnngggg time. So I will tell people, that yes, Charles Camsell's route from what is now Uranium City to Great Slave Lake on the Tazin and Taltson rivers is doable. To this day, I think my group was the only one who had done it since Camsell had done it. Similarly I have found no one who has the done the Mirror river in Saskatchewan.
When the rock you want to put a climbing bolt into is on publicly owned land (like a national park), then what you can and can not do is usually handled by local ordinance. For example, in the Elbe Sandstone Mountains in Germany, there is an ordinance (German source) which forbids to climb anywhere except on climbing routes designated by the park authority. So you can not just establish a new route because you feel like it. It also says that it is forbidden to damage natural rock formations with mechanical or chemical climbing aids. If you get caught placing a climbing bolt without permission, you will have to pay a fine.
So always check the local ordinances before you engage in any outdoor activity to see what you are and are not allowed to do. Never assume that just because something is allowed (or tolerated) to do in place A that it is also OK to do the same thing in place B.
Usually yes. However, the rules of climbing and of course the laws of the country must be respected.
You explictly say "next to an existing route" so I take it for granted that climbing in the area is not forbidden. That is a whole different can of worms.
Be aware that local climbing rules (or even the rules of the Mountaineering association of the country) may require a minimum distance of a route from an existing route. A non-conforming route may be destroyed by the local custodian. Here's an example of legally binding rules in the Czech Switzerland region.
Similarly, you cannot place bolts into existing routes (the original authir decides which protection belongs there, outstanding cases may be resolved by the local committee).
You have to respect the local sport rules that state the minimal vertical distance between permanent protection points.
You have to respect the local kind of protection if it is required by the rules (i.e., rings in the sandstone).
You have to respect the local sport rules about how new routes are to be created. Some areas require new routes to be done from the bottom. No pre-placing from the top.
Offending routes may be destroyed by the local committee/custodian.