Failure is not an option. It would be best to limit change to only those areas where there is very little risk at this time.
If New T-Mobile messes up the network integration (looking at you Sprint Network Vision) in the middle of this virus crisis, there will be hell to pay. Large numbers of people are dependent on their mobile phones, hot spots, and internet data connections right now for work, school, news, shopping, entertainment and just to keep contact with work, friends and family while they are stuck in their homes. If connectivity breaks, they can no longer communicate with the outside world. They also cannot run to a New T-Mobile store to get a bad software push to their mobile phone fixed right now so they better be careful with changes on the mobile device side of the network.