Adding Instant Yeast to dry bread mix for later use
Active dry yeast will lose quality quickly once it is opened. 

When you portion the yeast into your flour it will be exposed to oxygen and moisture from the air and flour. Even in vacuuming out the air there will still be some moisture in the flour. Some of the yeast will come out of dormancy and will consume their adjacent food and die.

How much yeast you lose will be variable- probably dependent on how fast you work, how well your vacuum sealer works, the ambient humidity that day, how long and at what temperature the mix is stored before use, etc.

There are plenty of anecdotes of regular people and even pastry chefs leaving yeast at room temperature for a few days with no loss of quality. It is hard to find scientifically observed shelf life numbers because the recommendation is to refrigerate or freeze yeast immediately upon opening. I suspect that it will be hard to find a definitive answer that fits your specific use case.

If you can portion your yeast in an environment free of moisture or air, if your customers will be using your mixes within a few days, or if the mixes will be refrigerated or frozen you should be fine. Otherwise your mixes will sometimes fail to rise.