Cancel Runnable in Execution Engine

Using com.inductiveautomation.ignition.common.execution.impl.BasicExecutionEngine is it possible to cancel a runnable that was submitted with executeOnce?

Only if you keep a reference to the ScheduledFuture<> returned when you submit the runnable, and you must use the 3-arg overload version of the method to get the Future.
If you use the register*() methods, you can use the owner and taskid strings to cancel it.