From what I understand the Wagon's Master Cylinder and Sedan/Coupe EX Master Cylinder are the same. You already have the correct proportioning valve for the front wheels in your ABS solonoid unit, So not only can you not change it but it would make no sense to do so.

As for bleeding the brakes. The best source for you to check with would be a service manual. The Brake fluid in the ABS solonoid assembly and pump are completely seperate from the fluid in the brake system. Bleeding it should be absolutely the same as bleeding any normal non-ABS car.

The brake fluid in the ABS solonoid assembly and pump is just for the valves in the ABS solonoid so it can acctuate them when it's necessary. You shoul never have to bleed that system or open it for that fact of the matter. It's a completely sealed off system.

But if you want to flush the brakes system I would consult the manual before begining. It should not be an issue because or my experiance in ABS brake systems and their design but maybe there is something special I don't know about with the 4th gen Accord. It's better safe then sorry. I always consult the Service manuals before begining work on a vehicle I'm not familiar with.

Good Luck