Custom mode is unlikely to be implemented in the initial versions of NTM v3000.
Implementing it shouldn't be a huge hassle, though. Many required features are already (half-)implemented. For example, things like changeable even/odd area sizes are implemented, but they require further refinement because the game is currently unaware of arbitrary maximum subarea numbers in some parts of the codebase.
Custom mode is unlikely to be implemented in the initial versions of NTM v3000.
Implementing it shouldn't be a huge hassle, though. Many required features are already (half-)implemented. For example, things like changeable even/odd area sizes are implemented, but they require further refinement because the game is currently unaware of arbitrary maximum subarea numbers in some parts of the codebase.