If your Organisation is in a tiered environment where your membership numbers are automatic and set from one of the tiers above, these options will reflect that tier and be locked down.
COPYING A MEMBER
If a member record is copied and Automatic Membership Numbers is set to yes, a new Member Number will be assigned.
If a member import contains an existing Member Number, the member will retain the member number imported regardless of whether Automatic Membership Numbers is set to YES.
If a member import does not contain an existing Member Number, the member will be assigned a new member number if Automatic Membership Numbers is set to YES.