This is likely how it will be during the transition, but based on 3.5 nd 4eEssentials.5, a few months in, you're just not going to get bring in any of the old stuff at a new table. As much as we keep saying we're going to use the old stuff, we keep... not doing that.You don't have to change your Warlock. Do you feel you have to? Is your DM going to force you? Just talk to your DM and let them know you'd like to play it as it has been. It breaks nothing!