We haven't had to add a new diagnosis, but we have updated our ds' IEP without having the full team meet - in our school, if the change was something that the full team agreed on, the change could be made by requesting it via phone or email, the school SPED staff member updated the document, and forwarded the update to us. The times we did this were when we wanted to add or clarify an accommodation.
In this case, I would start by thinking through what accommodation you'd like to have to avoid misunderstandings/misinterpretations of homework assignments, and are there any other accommodations you think should be added for CAPD? If you know what you want to ask for and it's straightforward, call whoever coordinates the IEP at your school and ask if it could be updated without a full team meeting. If you're not sure what to ask for or want to have a brainstorming session with teachers etc, call a team meeting for the update.
FWIW, I think that with the added diagnosis of CAPD you might want to add not just the diagnosis but some descriptive wording to the IEP that explains the impact of CAPD. I don't have an IEP form in front of me at the moment, so I don't remember which part you add that type of info in, but if nowhere else at least in the parents' remarks.
Another upside to having a team meeting for this is it gives you an opportunity to talk to ds' teachers and the SPED staff about how CAPD impacts your ds in the classroom.
Good luck!
polarbear
