If you are the guy with the temptation to go for the easy joke, this may be extraordinarily difficult, since as GM you really have the opportunity to set the tone.
Maybe you need operant conditioning. Every time you go for the easy joke, throw a token in a jar that the players can use as a bonus of some kind. Make them the arbiters, so they are both watching for you to slip up and tacitly monitoring their own behavior.
Maybe you need a way to express this stuff directly. Sometimes playing an inherently over-the-top setting absolutely straight is just not viable, and injecting a little appropriate recognition of the absurdity is both a relief and helps maintain focus. Maybe have a comic relief NPC, a guy who recognizes the ridiculousness, a sort of court jester, and use that guy as your mouthpiece for that stuff.
You've made two key changes:
- Allowing multiple combat half-actions per round
- allowing movement to be replaced by a non-movement half-action
The primary factors I see are:
- increase in Psyker offensive capability (Most of their offense is more powerful than their allowed weapons; it gets worse under RT or DW, due to a different psychic system)
- decreased access to defenses¹
- decreased emphasis on movement²
- increased emphasis on non-action defense (IE, cover)³
- breaks the equipment bonuses
- decreases incentives to use burst and full-auto autofire modes
- cybernetics and talents with extra half-actions become devalued⁴
- initiative becomes more important⁵
- Ganging up becomes less essential⁶
¹: Since one gets very few defenses per turn, this change of yours makes them less valuable, by allowing them to be overwhelmed faster.
²: The current system makes movement a valuable and essentially irreplaceable part of the round; take it or not, it's lost if unused or unusable. It's not terribly realistic, but is very cinematic. And DH, RT, and DW are all intended to be very cinematic in tone.
³: At present, especially for melee, active defenses (dodge and parry) are quite valuable; cover is less so, but not enough to render it useless. When one allows replaceing movement with a second attack, cover suddenly becomes MUCH more attractive, as it's an assured penalty to be hit, instead of a roll by the defender... but it also reduces drama.
⁴: At present, the only way to get a second attack is expensive talents and/or cyberware with inexpensive talents. If a character can just hole up in cover and double shoot, these talents are far less valuable, making the Assassin and Guardsman's additional combat actions less useful.
⁵: Further, by allowing the etra attacks, you can run a target out of actions sooner, as well, so initiative becomes more important to prevent having actions drained in defenses.
⁶: Ganging up is the great equalizer in RT and DH combats; it's how one overwhelms defenses. Given that every character can defend once for free, and once by aborting, if you can attack twice, you've just eaten both defenses this round, meaning you only need one attack from a buddy to get through. The norm is that you need two buddies to negate the defenses, or one buddy with a multiple attack talent.
It sounds like you made these changes with rank 1-2 characters... it's going to be more profoundly off-norm or higher rank characters, as normal slow growth of actions is made to feel even slower by providing far less of a bonus over not having them.
Best Answer
Yes, There are some changes but they are minor and small. As 2nd Edition is just a re-made and better made version of 1st.(That is up for debate but I'm not here to argue.)
If you have ever ran any 3.5 modules in Pathfinder it'll be quite similar. Use logic when the stats don't completely match and you'll find it works quite well.
In short: Yes they are compatible, as are most 1st edition to 2nd. Just be prepared beforehand.