I don't see a problem using display to change the displayed tense -- but only where the context logically has pushed the tense out of past-tense already and past tense would just sound wrong, not in cases where changing tense would change the meaning.

eg: changing "I did this" to "I will do this" with display would be a forbidden meaning change.

Changing "I planned &lt;I did this&gt;" to "I planned &lt;to do this&gt;" with display would be an appropriate use of display, but only in sub-statements since only sub-statements should be able to have a future tense.

From the timestamp requirements:

* MAY be a moment in the future, to denote a deadline for planned learning, provided it is included inside a SubStatement;
* SHOULD be the current or a past time when it is outside of a SubStatement.