Does the registration of aws organization affect existing services?

No, it does not affect services at all. You have to be careful with:

• Existing SCP in the new organization the account is joining to, as this can setup some limits that breaks some permissions, so, join the account to an OU without SCP, try everything and them move it to the final OU
• If you're moving from a previous ORG and you have things shared using RAM and organizations, this will break as soon as you unplug the account from the old org, if this is the case.

Best,