Trunk Group1 is now your PrimaryLine, so its DigitMap is now Mpli. Anything in Mpli can be dialled without ** codes. If the two DigitMaps were very different, then you could lose the ability to dial some Mli type numbers without **8 if you don't put Mli into Trunk Group1's DigitMap.
In practice, if the two DigitMaps are somewhere near default, then Msp1 covers most of Mli anyhow. Also if the xx. rule and/or the [^*#]@@. rule is in Msp1, then all numbers will be matched, but a 10 second delay might happen.
Best practice is probably to put both in like so:
((Msp1)|(Mli)).