It's possible to enter lewdomains without having the code in your grimoir. For this you need to open any portal and then put in the code for another domain. Doing so will not result in a change of portal color, but the portal will take you to domain of the code you put in.
I think this might be a bug, although I believe it could be an interesting feature if the game acknowledged it properly.
I did this on android. This worked with all domains up to icy chains, and presumably would work with the gate one too. This bug caused me to complete the story wrong, now breaking the seals was mostly one long conversation.