Section 34-6-20 does not apply if the applicable gift instrument indicates the donor's intention that net appreciation must not be expended. A restriction upon the expenditure of net appreciation may not be implied from a designation of a gift as an endowment, or from a direction or authorization in the applicable gift instrument to use only "income", "interest", "dividends", or "rents, issues, or profits", or "to preserve the principal intact", or a direction which contains other words of similar import. This rule of construction applies to gift instruments executed or in effect before or after the effective date of this chapter.