I'm not an oboist, so take this as general woodwind information. I hope I'm not telling you anything you already know; I'm sorry if I am.
A woodwind instrument is designed to play at a particular pitch level, such as A=440. What one means by that is that the tone holes are spaced so as to create an even scale at a particular pitch level. There are specific ratios that need to be maintained. (This is a simplification, of course.)
If you attempt to play an instrument designed for one pitch level at another pitch level, then you introduce distortions to the scale. The ratios will be off. The scale will be uneven: some notes will be sharp, others will be flat.
Brass instruments have slides to adjust each valve. Woodwind instruments don't.
If the difference is small -- say, trying to play an A=442 instrument at A=440 -- you may be able to get away with it by making changes to the reed and the embouchure, and perhaps with changes to the bore or tone holes by a trusted repairman. Other oboists can help you with the details of whether or not this would work; and if so, how well and what to do about it.
If the difference is big, it just may not work at the desired pitch. The instrument may be best left for playing at the pitch for which it was designed.
In the bassoon world, our instruments last much longer than oboes, but there is a cutoff for how old an instrument can be played in a modern orchestra. Bassoons older than about 115 years were usually built at too low a pitch to play at A=440. When shopping for used instruments, we also have to keep in mind that instruments may have been customized for the needs (or quirks) of an individual musician.
Personally, I wouldn't want to fight an instrument with an uneven scale. Playing the oboe (or bassoon, my instrument) is challenging enough as it is, without introducing the added variable of an uneven scale.
I guess it depends on how high the "relatively high pitch level" is, and what happens when you try to adjust to it.
I hope this helps.