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From my interpretation of how being a Psyker works in the 40K Universe, having a connection with the Warp affects you both mentally by giving you psychic powers; and physically, the same way that constant exposure to the sun can give you a tan (as a very basic example).
In a game of Dark Heresy, I have a Servo Skull, that was made from a dead Psyker, that was killed by their own Psychic Surge. Is there any chance that this skull might still carry some kind of psychic or warp signature?
Servo skull: It could have warp residue but not necessarily, it depends on how powerful the psyker in question was. probably a Eta level psyker skull would leave an imprint but a Kappa level would not.
Regarding your title question: psychic abilities can be used to alter your physical properties, however this is normally the result of a conscious action of the psyker in question. It can also happen subconsciously as when Zarahiel bolstered his stamina during his trials to become a space marine. Every time he was almost exhausted, he would gain a boost and could keep running longer than his cousin Nemiel. This is also how the chief librarian discovered Zarahiel was a psyker.
Every time a psyker uses the power of the Warp, he looks into a gaping maw of Hell... and sometimes the Hell looks back! Psykers are not hated because of their power, but because they can, totally accidentally, bring the death and destruction to everyone around. Look at the Dark Heresy Perils of the Warp table - if you have to roll on that table, you are lucky if you die... if you are not, you can doom everyone around you (of course, there are lesser effects - for example, you might start growing a new pair of arms out of your ass, which can be handy to scratch that itchy place on your back).
Now back to the other part of the question: In the 40k universe even not warp-sensitive people can affect reality on a small level. There are dozens of weapons and armours that are better because they've used to belong to someone famous - it is not only because those items were made better for some old hero, but rather because this old hero left some of his/her courage and spirit on his favourite sword. The same rule goes for the Chaos-touched weapons, as it was greatly displayed in the "DOW II - Chaos Rising" videogame, where you could find more powerful weapons, which were unfortunately slowly corrupting your team.
And now, you have with you a skull of someone who has been DIRECTLY touched by Chaos..,.
