It is not recommended because flushing by printing is not as effective as using suction or extraction to clear a clog. Flushing by printing is designed to use a cleaning fluid to clear out an ink channel. Also, we believe the best practice is to not over-stimulate a nozzle when it is clogged because doing so is a risk to permanently burning out a nozzle.
If an ink channel is clogged, or there are one more nozzles that are clogged, or there is a clog behind the nozzles and normal printing does not clear it - then printing PiezoFlush may be similarly non-effective. Having said that - there are people who have used PiezoFlush to print through problems.
Using suction or injection to pull or push PiezoFlush is done with great force in comparison to the tiny pressure produced by stimulating the print head nozzle to expel tiny ink droplets. If the nozzle can not expel ink by printing, it may not be able to expel the ink that is in front of the PiezoFlush in order to get the PiezoFlush to the clogged nozzle.
So it is a matter of physics as to why we make that recommendation. Using the small format cleaning kit should not be done with "great pressure". I am only saying that the physics of using pressure by INIT FILL or injection is so much greater than the force generated by printing.
Hope that clears up our best practices recommendation for clearing clogs versus flushing out an ink channel to change ink types.