Yes, you have surmised correctly that the endorsement does indeed make the injured condo unit owner an "insured" under the policy of the Condo Trust and hence excluded from the Medical Expense coverage under the Trust's policy.

 Liability coverage is third party coverage and does not provide first party coverage to the insured. The liability section of the BOP form provides coverage for liability sums that an insured is legally obligated to pay as a result of "bodily injury", "property damage", or "personal and advertising injury" to which the insurance applies. Under B. Exclusions, there is an exclusion in paragraph 2. Applicable To Medical Expenses Coverage excludes expenses for "bodily injury": a. To any insured, except "volunteer workers".

 The Condo Association Coverage Changes endorsement adds that the condo unit-owner as an insured for liability covered by the policy, but the exclusion for medical expenses coverage to an insured would apply and no medical payments coverage would be available to the insured.