I'm sure it's fine to undo a bit of the braid. Your plant still looks flexible.
Secure the top braid with a twist-tie, let the plant grow about six inches or so,
and then braid the new growth. Secure the top, then repeat the process.

That said, I'm the worst person to ask about braided Pachira. You see, I
don't particularly care for braided Money Trees. More often than not, one of
the trunks will succumb to rot, jeopardizing the other trunks. I *have* seen
braided Pachira thriving...when planted in the ground! ;) But I usually tell folks
to select a Money Tree with a really healthy trunk so that they won't have to deal
with die-off down the road. The fact is, many people grow these plants in mucky,
wet, peatmoss-based soil with terrible drainage. Then, they tuck these plants
into a dark corner, or in a room with the shades drawn, and begin to over-water.

Sunlight, soil with good drainage, and proper watering will make all the difference.

Josh

Here is a link that might be useful: Pachira aquatica (Braided Money Tree)