Merge two manually adopted devices?

Hi. Apologies if this has been covered but I haven't found it or understood a previous response.

I'm a domestic user on a budget who bought a UGC and was impressed then bought a UX7 when I realised I was going to need more control over WiFi.

I had hoped to adopt the UGC to act as a router/firewall for my trusted network within my household setup but everything I've seen suggests this isn't possible as it is also a cloud gateway.

Am I missing something? Is is poss le to manually adopt the UGC to be run under the control of the UX7 console?

A bit more clarification as to what I'm aiming for...

I had a home setup that had to have the devices run behind an ISP router. I am now in the position that I can ditch the home router.

The plan is to use the UX7 as the edge gateway paired with another UX7 to replace the wireless mesh the the ISP router previously provided. Yes I know it's not the best way but I can't run cat6 in the walls anytime soon.

I'd also like to use the UGC as a boundary to protect the trusted network.

All of this is via manual adoption not cloud account.

Is there a way to move to this that doesn't require arcane knowledge?