Brand rules for an AI assistant: standing instructions or paste context each time?

I've been going back and forth on this for a small client setup. Some people put brand voice, banned phrases and past winning headlines into a project or custom instructions once, then just ask for tasks. Others paste the context fresh every session because they don't trust old rules to keep applying. My view is that the standing version wins for anything repeated, like weekly copy drafts, because the rules stop getting dropped halfway through a long chat.

I'd keep the numbers out of it, though. Targets change every month, and an old CPA sitting in the instructions quietly shapes every recommendation after it goes stale. Stable stuff goes in the standing setup, live numbers go in each request. Curious where others draw that line.

Agreed on the split, and I'd take it a step further: put the rule in standing setup, but leave the reason for it out. "No discount language, we don't run sales" stays true for a year. "CPA under $38" goes stale within a month, and the model keeps anchoring on it anyway. A dental clinic might keep "never promise same-day appointments" in its standing setup and put this month's CPA in the request itself. It also helps to ask the assistant to quote the standing rules back before a big task. If it can't, or it quotes something you've already changed, the old instructions are the problem.

Agreed on leaving the reason out. The thing with numbers is that the model tends to read them as a target to hit instead of a limit to respect. "Never promise same-day appointments" stays a rule, but "keep CPA under $38" turns into a goal the assistant chases even when it shouldn't.

Putting the number in the request instead of the standing setup doesn't solve it, because the wording is what decides whether the model reads it as a goal or a limit. Say a clinic asks for "CPA under $38 this month." The assistant can easily treat that as a target and raise bids on a term that converts poorly just to drag the average down. Try "$38 is a ceiling, don't buy volume that converts badly to stay under it, and tell me if the cap means pausing something." That gives it a clear role, and it makes the output easier to check, since you can see whether it respected the limit or just landed close to it.