We see in Star Trek III: The Search for Spock that Spock was able to perform a mind meld with McCoy to transfer his Katra to McCoy for later rejoining with Spock's body. This had an impact on McCoy's mind (which turned out to be quite humorous). My question is can a mind meld impact a person's psychology without transferring the Katra over e.g. could Spock perform a mind meld with McCoy and make him not like medicine and prefer astrology or something?
Yes, although not necessarily to the same extent
If you mean change their actual personality as Spock did to Bones, I can't think of an example. It's hard to say if Spock could make Bones love transporters and hate medice ... but if you mean impact their psychology to point of changing their behavor, Memory Alpha has several such examples:
(ENT: "Fusion", "Stigma")
(TOS: "Spectre of the Gun")
(TOS: "Requiem for Methuselah")
The Spectre of the Gun example seems to suggest Spock could fool Bones into hating medicine.
Also, both Sarek and Captain Picard in the TNG episode Sarek, Sarek's deteriorating mental condition, Bendii syndrome, results in losing the control of his emotions, and he inadvertently broadcasts his emotions telepathically until the whole ship almost goes insane, either by arguing, insubordination, harassment, and brawls across the ship.
In a desperate measure to deal with the situation of Sarek negotiating peace talks, Sarek mind melds with Picard to let Picard lend his emotional control to Sarek temporarily. Due to this mind meld, Picard succumbs to some of Sarek's most primal emotions for a short time, until Sarek completed the negotiations, when he boards another starship to return to Vulcan.
You could say that Tuvok's meld with the Betazoid Lon Suder affected both their personalities:
I'm not sure if this qualifies as a fundamental change in personality or just an alteration of the balance of components that were already present.