Until the Discharge Date and unless the Lender otherwise directs, the Guarantor shall not exercise any rights which it may have by reason of performance by it of its obligations under or by reason of any amount being payable, or liability arising, under this guarantee:

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(b) to claim any contribution from any other guarantor of the Borrower's obligations to the Lender;

(c) to take the benefit (in whole or in part and whether by way of subrogation or otherwise) of any rights of the Lender in respect of the Borrower (or any of its subsidiaries) or of any other guarantee or Security taken by the Lender;

Получать выгоду (преимущества) от каких-либо прав Кредитора в отношении Заемщика...?

shall not exercise any rights to take the benefit of any rights -- реализовывать права, чтобы реализовывать права

Alex16, у вас хороший вариант. Можно ещё (т.к. упоминается суброгация) взять "вступать в права"