That shouldn't be a problem. I asked Sound Devices and Sonosax this same question several years ago about recorders/preamps I have from them and they said it's fine. For example, on my Sound Devices MixPre 6, I have my channels set to phantom all the time (unless I'm using ribbon mics or other dynamic mics). I plug in the mics before turning on the recorder, and unplug them after the recorder is turned off. But I could just as easily leave them connected all the time. Sound Devices confirmed that this is perfectly safe; Sonosax did the same (I asked with respect to my M2D2 preamp).
The message I got from Sound Devices support went even further: "It's actually OK to just plug-in a phantom-powered mic to a jack with phantom power already enabled...but this method could damage a sensitive microphone. Your process is perfect - leave phantom power enabled and...plug-in mics, power-up MixPre, power-off MixPre, disconnect mics. No problem."