bitcoin core – The way to add a customized struct to PSBT and deal with transaction charges with two events utilizing BIP-174?

I’m engaged on a Bitcoin transaction the place two events are concerned. The purpose is to lock funds and create a customized struct within the transaction output. Here is how I intend to set it up:

First social gathering offers the funds and initiates a Partially Signed Bitcoin Transaction (PSBT) utilizing BIP-174.
Second social gathering will add a customized struct (presumably metadata or a selected output element) to the PSBT with out offering any funds.
I am questioning if the next is feasible:

Can the second social gathering add a customized struct (output or metadata) to the PSBT, whereas the primary social gathering is the one one offering funds?
Who will probably be accountable for paying the transaction charges? Will the primary social gathering bear all of the charges since they’re offering the enter funds, or is there a option to distribute this between the events?
Are there any identified constraints or finest practices for reaching this inside Bitcoin’s protocol and the PSBT normal?
I might recognize any steering on whether or not this setup is possible and easy methods to deal with charges and struct addition in a PSBT.