Do all requested changes need to be agreed before signing contracts?

Hi All,

I'm buying a new build property which is unlikely to be ready for at least another couple of months.
I sent a list of requested changes to the developer - some very minor (e.g. placing of sockets and light fittings) and some a bit bigger (moving doors and including extra storage space).
My solicitor has told me they've received the deeds etc and that the developers solicitors want to sign contracts this week.
I haven't heard any response on whether my requested changes are a) possible, and b) what the cost implication is.
Should this be clarified before signing the contracts, and if not, at what stage should be agreed?

Thanks for reading