Does renewing a plan, trigger the activation/deactivation actions?

A renewal triggers the activation, yes. So if they renew and it's configured to set a fields value it will override whatever you have set manually.

If so, is there a workaround?

It's doing as it's supposed to so not really. Only way would probably be to just use CB Auto Actions for this and add a condition to ignore setting the fields value if it's equal to 2. You might be able to use the below usage as well in CBSubs Fields integration to just leave it as 2 if set to 2.

[cb:if cb_role_assign!="2"]0[cb:else]2[/cb:else][/cb:if]

If you want to replace this behavior with CB Auto Actions use the below to act on subscription state changes.

Plan Active
Global
Triggers: onCPayUserStateChange
User: Automatic
Access: Everybody
Conditions
Condition 1
Field: Custom > Value
Custom Value: [var3]
Operator: Equal To
Value: PLAN_ID_HERE
Condition 2
Field: Custom > Value
Custom Value: [var2]
Operator: Equal To
Value: A

Plan Expired
Global
Triggers: onCPayUserStateChange
User: Automatic
Access: Everybody
Conditions
Condition 1
Field: Custom > Value
Custom Value: [var3]
Operator: Equal To
Value: PLAN_ID_HERE
Condition 2
Field: Custom > Value
Custom Value: [var2]
Operator: Not Equal To
Value: A

Be sure to replace PLAN_ID_HERE with the actual id of your plan as found in CBSubs > Plans.

That's an unsupported IF substitution syntax. Please read the substitution tutorial below carefully for supported syntax.

www.joomlapolis.com/documentation/279-community-builder/tutorials/18353-using-substitutions-throughout-cb

If it's truly empty then the below should work. If it's an integer field though it will already be set to 0 as its default value and can't really be empty.

[cb:if cb_role_assign=""]0[/cb:if]