How can investors switch from real estate to fixed term investments during their golden visa stay in Greece?

Sell the property, buy term deposit and inform again the Immigration Office about your actions.

On Sept. 4, 2021, a bill was voted by the Greek parliament regarding the entitlement of a third country citizen, holder of a valid residence permit, for investment in one of the categories of intangible assets as per provisions of Art.16 par. C Law 4251/2014, to liquidate the investment, in order to invest, within an exclusive period of two months, in another category of financial products or in real estate. The terms and conditions of the implementation of the above amendment will be settled through respective ministerial circulars. The above amendment could be applicable in your case, which is just the opposite but within the same content. If not then your lawyer has to submit an official question to the Ministry of Immigration and Asylum in accordance with the principle of equity and equal treatment under the same conditions.

It cannot be done; they would need to apply again like their first application.