It doesn’t work like you are describing with exchange migrations.
You set them up so they coexist - working together and move mailboxes, groups etc over whilst having rules in place to ensure mail flow, once that is complete and your happy it works, the rules are removed and the old one taken out of the environment
I have over 15 years system administration experience with a number of distributions of linux / unix and windows server, working for a large number of blue chip companies here in the UK.
Skill-List (Including but not limited to):
Windows 2000-2016 Server
Exchange 2003-2016, Office365
Linux / Unix Administration
SAN Storage (NetApp, EMC Clariion, HP MSA/EVA/Lefthand)
Server Virtualization (Vmware ESX, XenServer, Openstack)
Desktop Virtualization (Vmware View, Xen Desktop)
Application Virtualization (Thinapp, Xenapp)
Networking (Cisco, Juniper, HP, Extreme, Ubiquiti)
Firewall / IDS (Cisco, Fortigate, Juniper)
Backup (CA Arcserve, HP Data protector, R1Soft, Veeam)
Server administration (MsSQL, MySQL, Oracle (inc forms & reports), InnoDB, IIS, Apache, SCCM, WSUS)
VoIP Solutions (Nortel, Avaya, Shoretel, Asterisk, FreePBX)
Penetration Testing / Server Security/Hardening
WHMCS, DirectAdmin, cPanel, Webmin
AWS, Azure Config/Management