Car finance options

[contractor]

Hi.

If I put down a cash deposit on a new car and agree to finance the rest, can I decide the finance option later?

Can I agree manufacturer finance, then order car, and then seek a better rate from another source prior to taking delivery (4 mth lead time)?

[contractor]

Thanks. The reason I ask is that Halifax are offering 3.6% Apr but I need to have had a current account for 90 days. I've just opened one today.

I was hoping to do the deal with BMW and secure finance with a half decent rate and get the car ordered.
Delivery won't be for about 4 months due to lead times and by that time I'll be eligible for the Halifax product which would likely be a better rate. I would then use that instead