Tang safety Ruger 77's are 2 position by design and lock the bolt.
Tang safety Ruger 77's are 2 position by design and lock the bolt by design. MarkII with the safety on the bolt sleeve are 3 position by design and allow for opening the bolt with the safety on. Locking the bolt was long touted as a feature to ensure that the bolt would be in battery when the rifle was brought up to fire and the safety released. I'm very much inclined to agree. The unlocked bolt might, or might not, swing open just a tad if the bolt handle hits some brush or what have you.
My preference is the tang safety design. It is trivial to modify the tang safety so that it does not lock the bolt. So far as I know there is no advantage to a 2 position safety that does not lock the bolt. So far as I know Ruger has not advocated nor performed any such modification on the tang safety Model 77.
Folks can modify their own rifles in most any way that does not violate local, state or federal laws as for instance short barreled rifles, full auto and so forth. I'd suggest going with as intended by the maker for almost all purposes.