Attempts to add TM1RebuildDefault to the tm1p.ini fail.
Resolving the problem
The TM1RebuildDefault parameter was not officially added until version 9.4.1 FP3. It was first available in 9.4.1FP2 HF26. So attempts to use it prior to that version will result in failure.
If using FP3 or higher and having trouble getting it to work, be sure that all instances of Architect/Perspectives are closed prior to making the change in the tm1p.ini file.
Also note that unlike the TM1RebuildOption in Excel (which uses 0 or 1), the TM1RebuildDefault should be set to either T (true) or F (false).