Patrick, I dont know about changing dollars to cash but there's a limit before you have to report taking cash when you cash a check.
I remember cashing a large check once. I forgot to bring my backpack with me. The stack was way too big to put in pockets.
No way I was going to carry it out in a plastic bag. So I unzipped my motorcycle jacket, took out the padding and replaced it with pesos.
When done, I had more padding than when I started.

. No one asked me to sign anything.
A few months back I cashed a large check. This time I asked for $10K in cash. They made me sign a note which stated it was my decision to take the funds in cash.
I transferred the balance (higher) to an account in Uruguay bank. No one asked me about that.
Yesterday, I went to the bank to wire funds for a real estate purchase up north.
The bank asked me politely, (as in if I said no I wasn't sure if they would back off or not), to bring a document that showed the purpose of the transfer.
This wasn't an isolated instance. I asked my Cambio to transfer a paltry $1K 2 weeks ago for the down payment on this purchase and I was asked the purpose of the transfer.
Didn't sign anything though. I think they wrote it down as an explanation on something.
I get a chuckle when I look at HSBC's website.
They go on about how they have great offshore operations in Gurnsey (sorry--cant remember the proper name/spelling) and Uruguay.
When you click on the Uruguay part, it says how great the country is with a 50 year tradition of banking privacy/secrecy.
Wonder who HSBC is negotiating with with 50% of their offshore 'safe house inventory' on its way into history.