I'll try to explain this so it makes sense.
We contracted a developer for some customization. She created a full sandbox from our Enterprise production environment. Our Opportunity object was limited to 500 custom fields which we are quickly using and need more to finish the development, so we upgraded to Unlimited Edition.
Unfortunately, we didn't realize the sandbox wouldn't have the additional field limits because it's a copy of our original Enterprise edition. We do not want to deploy the new version yet.
An alternative we are thinking of is to create another copy of our new unlimited production environment that now has limits of 800 custom fields per object. Then deploying the developing sandbox, which will then adopt the Unlimited field limitations, then making another sandbox from that, so we can continue our development, then redeploy the copy of the Unlimited Edition of our Production environment.
If we do it after hours we are hoping no one will be the wiser. Here's my concern. Someone else told me that once we deploy the new version with customization into production and then redeploy the Unlimited production copy we made, the new customization will still be present in our production environment. Basically a mix of the old and new. Is this true? We want the additional fields in our developing sandbox, but we don't want any of the development we've done so far to be present in the production environment yet, as it is quite different and has a lot of automation from what everyone is used to and will require re-training.