There really are two approaches to take. The first, and obvious one, is that skill trait levels are absolute and that regardless of one's background a Great Marksmen is a Great Marksman and, luck aside, one would expect a competition between the two to be very very close.
The second, is that all skills (and potentially many gifts and faults as well) are modified by two scales. A geographic area scale and, if applicable, a temporal scale. These scales are defined by the characters background. A geographic scale may look something like:
A temporal scale (or technology level scale) works the same way. If Jane Doe was an vehicle engineer on the backwater planet of "Earth" and only had a Superb master of internal combustion engine based vehicles, when arriving on the planet "Eco-9" her ability to fix the fully electric or hydrogen powered vehicles would be impaired (-1), although some aspects would still be very familiar. When arriving on the planet "Miraculous" where thought bubble transports are the norm, Jane may be several (or many) levels away (say -5), but an exceptional dice roll may allow her to fix, repair, or modify the simplest of problems of the bubble transports - after all the bubble transport probably still has something to steer with, some way to accelerate, and some way to brake and something that powers them. Conversely, for someone on the planet "Miraculous" to strip down and rebuild an antique internal combustion vehicle just unearthed at an archaeological dig, may be hard to do, but for Jane, it would be a piece of cake. Even Superb vehicle engineers of Miraculous have long lost the hands-on expertise for internal combustion vehicles (they would be at the -5), but for Jane, it is her native technology level.
Such scales can also readily be applied to Gifts (and Faults) such as Reputation, Authority, Wealth, and many others.
In a pulp setting in a global campaign set in WW1 or WW2 using a geographic scale can remind characters of how far afield the adventure has taken them, provide new challenges, and help bring the sweeping scope of involvement in a global conflict to the game.