From my post of the Powell Trumpets facebook page:
Practicing with a practice mute certainly isn't ideal, but it is a necessary evil in our world. Long weddings, church services, being quiet backstage or in the pit, etc. We have to get the job done, and using a practice mute to keep the chops going is a must. Sometimes we find ourselves in hotels or at home late when practicing must be done and we reach for that mute.
Practice mutes seem to have the same disadvantage, to varying degrees. They all add resistance to the trumpet that the player isn't used to performing with. All mutes do this, really, but practice mutes do so than others. This added resistance tends to cause players trouble through intonation issues, response problems, and simply not being able to blow through the trumpet like we are accustomed to.
If a person has to do an extended practice session using a practice mute, (the tip you have been waiting for) then I suggest to also wear earplugs!! I know this sounds ridiculous - you're probably thinking "why would I need earplugs when I'm playing with a practice mute?!" The earplugs allow you to hear your inner-ear sound with much more presence, much like talking while closing your ears with your hands.
Hearing your sound more presently via the earplugs will allow you to back off a little while you play with the practice mute. This will lessen the negative effects the practice mute can have on your next performance. Try it out!