I would suggest inviting, or "recruiting" the teachers you are leading to help you with working out the direction in which you hope to move from an emphasis on "procedural efficacy" toward an emphasis on "conceptual understanding." Try to frame it as a "team project", explicitly recognizing their experience and first-hand perspectives in the class-room. Don't frame the changes in terms of their failures; rather frame things as you and they being at an exciting time in math education, based on much research, that all of you can participate in helping your students master mathematics, not just procedurally, but also conceptually!
I emphasize the above mode of approaching your teachers, because very few "team members" warm up to anything they are told is going to be "shoved down their throats", whether they like it or not.
E.g., start asap setting up a "workshop", break it into groups of teachers, and have each group evaluate relevant studies/research, and/or possible alternative concept-based texts, to report back to the whole group to summarize. Ask them for examples in their own teaching, in which student's seemed to grasp conceptual understanding beyond just mere procedural efficacy, even when having used the former texts. Chances are there are already a few teachers who have springboarded off the given text, at the time, perhaps discovering greater mastery among their students.
Try to do such workshops and updates on the new changes, and text selections, in the least threatening manner to them as possible. Be enthusiastic, respect their work, express confidence in the newer approach, and express utmost confidence that they have all the support they need (more workshops, etc.), and adequate experience, to make the new approach successful: More rewarding for both the teachers, and the students.