If you let another amateur radio operator with additional qualifications than yours control your station and operate under your call sign, what operating privileges are allowed?

When your station is operating under your call sign, the privileges are tied strictly to the qualifications associated with that specific call sign. Even if a guest operator holds a higher class of license, they cannot use those extra privileges while transmitting under your identity. The governing rule is that the call sign being transmitted dictates the maximum allowable operating privileges. If the guest operator wishes to utilize their advanced privileges, they must identify the transmissions using their own call sign rather than yours.