Writing that 5 to F038 0000 should work the same whether the command is coming from some php code or PAC Manager or a bit of OptoScript running on the same device. Of course, you have to be careful when writing/running code that does a "reboot thyself" because that can be tricky to troubleshoot, and even wrap your mind or brain around.
For example, you'd only have a split second to see that CM_MMP_Result came back zero (I'm assuming you're using the PAC Control debugger to see that?) since the device should be busy rebooting itself and no longer communicating for a few seconds. The strategy itself will then be blown away, at least out of RAM.
Are you stepping through this code to troubleshoot in PAC Control's debugger? Can you see the device in question? I'm guessing that eventually you plan to have your strategy options configured to store the strategy to Flash Memory then autorun? (That way after the logic to reboot executes, and the reboot finishes, the strategy will be reloaded from flash and start running again at block 0 of the Powerup chart.)
Any more details you can provide about your bigger picture/situation would be interesting to know, and might shed more light on what could be happening there.
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