Most of the B&G rolairtrol separators we get in lack the mesh plate that serves as nucleation sites for the air to disentrain. Aside from the tangential connections, they are an empty vessel no different than a chunk of pipe. Create a low-velocity section like LittleInch describes and it will do the same function of allowing bulk separation of any air brought through the system. The accompanying B&G auto vents just have a calibrated ball check in them that will fall open when there's a sufficient amount of air below the check to no longer suspend the ball- that's why they spit and spurt during startup when they're actually working.
Your 6-month "temporary" setup includes seasonal changes that may impact usage of the system substantially, I'd be very hesitant to agree to "temporary" accommodations without seeing a year or two of thermal data to ensure with high confidence you'll only be seeing a small temperature change during the entire duration (and an additional 6 months of buffer time for project delays).
The safer bet vs. removing the tank would be to check that expected temperature change and size a tank at the absolute minimal to account for your corresponding volume change. You might be able to get by with a tank small enough to fit, and cheap enough to not run up the budget, which will avoid all of the issues presented in discussion already.
If you're taking sections of pipe offline for rework and putting them back into service an air separator should not be removed. The only way you'll get away with no air separator is if you can guarantee no leaks, no low pressure events, and no service valves being opened for the duration of the "temporary" work to ensure you're not introducing large amount of air into the system.
And I keep writing "temporary" in quotes because temporary solutions that work have a bad habit of being left in place, or worse, becoming normal practice.
