I've fitted my kitchen with beech worktops and I was recommended to use boiled linseed oil. Now I have read that Danish oil is the preferred oil for kitchen use, and it dries quicker. The linseed oil has given the wood the colour I wanted so it would be a shame to sand it back, so, can I use Danish oil on top if the first few coats of linseed?
Yes, by all means. You might want to test a spot (not for "will it work" - it will - but for any possible color issues.)
As for what you have read, consider it an opinion, nothing more - if you like what you have, boiled linseed is just fine. Apart from some potential risk to tree nut allergy sufferers, walnut oil also works nicely and is a drying oil. Pretty much all the oils can be recoated and/or coated over one another with little issue if the previous coat is dry/cured.