Rebranding of Company | Rename / Migrate / Trust entire Domain

hi. ReverseSwing​ find below high level response to your query's

What should our approach be to minimize downtime, smooth transition with minimal loss of data?

• The recommended approach is to build a new Active Directory forest (Healthy.Org) and run both environments in parallel with a forest trust in place.
• Use a phased migration (department by department) rather than a big-bang cutover.
• Core services (Exchange, PKI, ADFS, Horizon VDI, DFS) should be stood up fresh in the new environment, while user accounts, mailboxes, and profiles are migrated in controlled batches.
• This minimizes outages, keeps users working, and allows rollback if issues arise.

How much time will this take? ( tentatively )

• Preparation & new domain build: ~6–8 weeks.
• Pilot migrations: ~2 weeks.
• User and service migration in phases: ~6–8 weeks.
• Application reconfiguration & cleanup: ~4–6 weeks.

Realistically, you should plan for a 3–4 month program end-to-end, depending on resources and smart card re-issuance.

Is using ADMT tool helpful?

• Yes – ADMT is very helpful to migrate users, groups, and workstations while preserving SIDHistory so existing file shares and roaming profiles remain accessible during transition.
• Even if you don’t want to “bring old data,” using SIDHistory during the migration phase avoids major access issues. Once migration is stable, SIDHistory can be cleaned up.
• Without ADMT, you’d face manual account recreation and broken ACLs, which would cause more downtime and data access problems.