No one will be able to give you a certain answer but only a probability.
The chances of a tube containing Flash Powder detonating if you shake it are low, higher if the tube is a plastic such as PVC, but still low (although why Flash Powder is being encased in a plastic tube is beyond me...). However, as with all things in pyrotechnics, it's not a certainty that it won't. Basically don't go shaking the hell out of a salute, but if it gets shaken around a little in the back of your car on the way to a display site, it shouldn't be a problem.
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