As long as the pH and other components of your tap water, are not significantly different than your tank water, and it dechlorinated, there shouldn't be a shock.
If, because you are slack doing water changes, and the pH of the tank is 6 (for example), and the tap is 8, the this could be a problem.
Before shipping I usually take a bucket of tap eater, dechlorinate it, and set the bucket in a sump of whatever fish I'm shipping,to equalize the temp, and use that water for the bags.
And I also have sponges always laying around in sumps, I cut a small piece of sponge and drop it in the bag to provide a beneficial bacteria source to help control ammonia, and nitrogen.
There is some controversy in this idea, however, because in the process of metabolism by the bacteria, there is always a biological oxygen demand (BOD), and may use up more oxygen than its worth.
Buphy, please let us know how your endeavor works out, does the package arrive on time or late, how you did it, and whether it ends good or bad, not to be criticized, but as a learning/teaching experience for all.
Not long ago, I sent some Lepidiolamprologus elongatus fry to a number of people, they were maybe an inch, and tried to use breathable bags. By the time they had reached destination, most bags were only at best, half full. The tiny fry spines had punctured all bags. My next shipment used regular bags without a hitch...we live and learn.