This is an old old technique (I think it was first talked about way back in OH 1.6 IIRC). It can be effective but it can also cause problems. For example, the next time you update OH, your changes to the openhab.system file will become lost and you’ll have to make the change again. In some rare circumstances you can lost some files if power is lost or something else goes wrong during the move. These are just a couple I’ve seen with this approach.
There is a simpler and less disruptive approach though. You can use Delay Start [4.0.0.0;5.9.9.9] to do this in a less disruptive and selective way. You likely do not need to prevent all rules from running during startup, just those that are generating errors.
This rule template lets you select those rules you don’t want to run during startup. It will disable those rules until runlevel 100 plus a definable delay before reenabling them. Disabled rules do not trigger and you can disable managed or file based rules.
Only for the Exec binding. @stefano73 is using the executeCommandLine which does not require whitelisting.