Only in case of ESSENTIAL changes, duly thought through, that do not substantially modify the project

• officially, in writing
• before the change takes effect
• at least one month before the end of the implementation period
• signed by the legal representative of the beneficiary organisation
• together with all necessary evidence / supporting documents

See also

Minor Changes do not require an addendum. These require a notification to the Contracting Authority asap.

Substantial Changes require an addendum to the Grant Contract. Formal request to be sent to the Contracting Authority (justified in line with the objectives, as initially signed)