groovy script to restrict a solicitation close date from being backdated creating amendment?

Summary: How to write groovy script to restrict a solicitation/negotiation close date from being back dated while creating a solicitation amendment?

Content (please ensure you mask any confidential information): We have a requirement where if we have a close date of 2 weeks from today as Solicitation/negotiation close date, if I try to amend negotiation and change the close date earlier than the previously provided date it should prevent me. How to write a groovy code for this or if there is any other method?

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