Adding 401(k) to Profit Sharing

We have a new plan we are setting up as profit sharing only in 2025. They will be adding deferrals/SH Match effective 1/1/26. In an effort to stream line things, can we add this in the initial Plan document (indicating that the CODA portion isn't effective until 1/1/26) or do we need to do a separate amendment to add this?

I've done it before. I don't see any issue.