Registrar and celebrant?

Never seen it done like that on the same day at the same venue but I have photographed one where the celebrant led part was a pagan handfasting ceremony by a pagan priest out on the lawns surrounded by trees with all the guests in a circle. So it was very different from the ceremony inside 15 mins ago. Which I think may be an issue for you with some guests possibly thinking "what's the point in doing it twice"

I would suggest an option for you would be to have the "official" ceremony earlier at the venue with just close family before all the guests arrive and then have the celebrant lead ceremony later. That way as far as the guests are concerend it will be the main ceremony and you could also keep your traditional entrance and so on.

For the earlier ceremony you get any close family photos done then and save time later.

Had been thinking about doing this for ours next year and I've read that it is technically possible in our borough (where we both live and are getting married), but definitely the more expensive route. To achieve this now we'd also have to move the timing of our registrar to earlier in the day and I don't know if it's worth it or possible without incurring a cost. We're giving notice in October so will ask the necessary Qs then. If we can't make a switch then I'll be requesting to fill out the ceremony with the registrars with music and readings from family instead to make it more personal.

It's the only thing I wish I had known more about before spending the money on the registrar and they sure don't make it obvious that you have choices.

"I'll be requesting to fill out the ceremony with the registrars with music and readings from family instead to make it more personal."

That is a great way to personalise it - you can also write your own vows - so long as the contractual words have been said before or after.

But just a little heads up for you. The registrars usually will have time limits as to how long they spend with you so be sure to check that with them. If it is not a busy time and they do not have another wedding after yours then they will be more relaxed about it.

We're doing our legal bit early so we can have our friend as celebrant (we've been calling him our officiant even though it's not official lol) - I was initially against it but got my mind changed by others who have done it! They said these things that convinced us/mainly me as FH was already chill about it that it would actually be really lovely...

Pros:

Takes the stress out of the wedding day because you're already married, no drama if you slightly mess up your words, no paranoia of being jilted

My mum's going to walk me down the mini aisle for the legal one so she feels special and gets to do the dad role too

Good excuse to get a nice pretty dress for the legal one (not spending wedding dress money again though but going for something very rewearable!)

You can use your "almost went for" songs

You can buy a supermarket (or fancier if you like) bouquet of flowers in your "almost went for" colour scheme

Nice outing for immediate family/whoever your witnesses are to sign the papers and go for a lunch or dinner after

Officiant can be whoever you like with whatever vibe you like

No awkward stopping part way through the ceremony do read the paperwork and do the signing which keeps the flow and vibe on point

And my favourite... "getting married is fun, so if you're only going to get married once then why not get married twice!"

Cons:

The day on your certificate isn't the same as the day of your celebration. We're actually erring on going for our current anniversary for our legal one so it sort of signals the end of that anniversary and then the main wedding day will become our new anniversary)