Well if its any consolation I find that the hardest part of converting to more abstract and rules lighter games starts and ends with the GM. The players generally will jump at the chance to do anything narrative given the oppertunity. Most groups have power gamers and crunch based players, but I find in as a whole the GM's tend to be the biggest arbitrators of that style of play and sort of lead by example and setting a presidence to "we stick to the rules".
Warhammer I think if analyzed as a mechanical system wouldn't hold up very well and is full of holes. Things like Action Card and profession traits for example are part of a very losely fitting quasi mechanic that is intentionally vague and often left to GM discretion. Things like Corruption rules and social encounters all hint a the fact that if your looking for tight fitting rules you will be disapointed.
That said though its not without rules either and its important to note that while there is plenty of abstraction, the intent of the abstraction is not to go back and break rules or live outside of them. There are rules for example for what happens when you critical hit a henchmen (they take damage equal to the critical hit strength), and so you usually do have rules to fall back on. But the golden rule every good GM and role-playing system should follow is that the narrative always takes presedence over the rules and even in 4th edition which is about as crunchy a system you can get, in particular as it applies to combat, this is, in fact described in the openning chapter of the DM guide.
Role-playing games make for poor board games and as we discovered with 4th edition D&D rules even the most honest attempt at balance, structure and rules definition leaves the game full of unabalances and holes, but the mere attempt to cover everything closes many opertunities for narrative storytelling as players are less likely to accept the GM whim if they are accustomed to a game that has strict rules.
If I were you I wouldn't announce to the group "hey we are going to try something different, or Im going to infuse more of this kind of thing". Just suprise them and do it sporadically. I personally found that if I sat my players down and explain to them "hey Im going to do this", than suddenly the "rules lawyering" comes out. But if I just implement something on the fly, aka, they see it more in practice rather than a concept, than the resistance just vanishes and I think its because in the end the most fun thing to do is to encourage some of the more interesting narrated actions players perform because it has a more natural sense of basis in reality even if it is abstracted to a degree. I don't know if that makes sense but as an example, if I say "from now on a critical hit is a kill".. suddenly its a rule.. If I just mentally decide to do it and implement that into the game, no one seems to notice that I have created a new rule.. in particular when in certain circumstances I might decide (hey this fight is going to be too boring if these beastman just get their heads blown off) so I might instead narrate that half the beastmens head gets blown off and they are still charging!!.. Suddenly the scene is even more intense and freightning full of imagry yet the player still get satisfaction that his narrated effort was reward… but because I didnt announce it as a rule… no one is rules lawerying it and just playing off it.
Hope that makes sense but the simple way to look at it, try to make every scene awsome and encourage the players to participate in that by rewarding them.. but just dont make rules too defined and overt so that players arent trying to exploit your effort to create interesting scenes to make their results better than the rules could normally make them. In particualr when it comes to combat.