If market conditions cause asset values to change, the portfolio is re-adjusted (rebalanced) to once again meet the original, targeted asset allocation mix.
That was the original purpose of the Troubled Asset Relief Programme (TARP), before it was used to recapitalise banks, bail out carmakers and subsidise loan modifications.
The person who sets up the trust gets annual payments adding up to the asset's original value, plus a return based on a fixed interest rate set by the Internal Revenue Service.