The list is missing some very key points
13. database backups have to be done outside of office hours because everyone knows you can't back up databases whilst people are using them.
14. there are several databases that need backing up.
15. the actual switching over of user accounts following the backup has to be done outside office hours. Probably a weekend. You can't remote in to do this so the building will need to be open. This now involves at least a caretaker opening up for you and turning off the alarms. If you can get the caretaker to say they're not available, a senior member of staff may have to be inconvenienced. Won't work if your building is already 24/7 but worth a shot.
16. the risk matrix says doing this just before Xmas would be a bad idea, earliest point it can be done is the new year.
17. because of the size of the databases (you can pretend to discover this after you've been absolutely forced to do the work) means you need to order some new kit. At the very least some large external drives, possibly also some (additional) cloud storage, maybe even software. And if you really want to postpone the work, an industrial espionage proof top of the range secure laptop for backup storage and transportation. Also a fireproof safe to keep the laptop in. And one of those biometric eye-scanners to lock the room the safe containing the laptop is in.
18. in the unlikely event you get all that (because your boss is even more bloody minded than you are) or if you are forced to go ahead without all that kit (more likely) then do the work. Insist on overtime at the very minimum. And then, come Monday, make sure the system isn't ready and working. Prep a room as full of cables and flashing lights on important looking boxes as you can. Explain there's a hitch/problem/issue. You can keep this up for a while I'm sure. Once you've run out excuses then it's a question of time. Might be an hour.. might be a couple, the spinner / bar / countdown timer / other thing that might provide an idea of when it will be ready has stopped. Might be stuck on a large file or maybe the bandwidth is flooded.When there's absolutely nothing else you can do and you're being told to phone Microsoft/God/IT Support somewhere, make sure your support is in a time zone that isn't awake for several hours yet. That support may need to escalate several times. You can easily wait days for Canadian support to move from T1 to T3. If you're in Canada, make sure everyone knows your support is in Australia.
19. Always, always.. make sure you can put your own preferred system back on incredibly easily, after all the mess is because of management, you're the good guy in all of this.