Snapd has the concept of “snap interfaces”. Those are documented https://docs.snapcraft.io/interface-management/6154
In this particular case opera is very likely to contain a
home plug that can be connected to the system
home slot with a command
snap connect opera:home (the slot can be omitted in this case). This will grant opera access to all the non-dot files in your home directory.
The case of editing permissions associated with interface connections is far more complex so I will refrain from going there. It will most certainly require your own build of snapd so that rules added to your system will not conflict with the evolution of rules that constitute the rest of the snapd permissions.