Reset a Windows 10 computer and then get back in remotely

Not wuite sure, but I assume you mean, you reset the machine and after theat you can not initiate the RDP session?.
I just have a group policy which forces the rdp service to start automatically. This way I can catch an remote machine, even freshly installed. 

Yes, thats what I'm talking about.  What if its a computer on a network without a server?

Not that I know of unless you could figure out a way to wedge something into the built in recovery image...
There are many ways if you have someone onsite capable of following basic instructions that can add something...
Not sure how you could use any group policy since a freshly reset machine isn't joined to a domain...

that more bad, because you do not have GPOs.
If the services are disabled by default (they are disabled), you do not have really a change out of the box.
Preconfigured Windows images possibly.
Does it happen so often, that you have to reset a Win 10 machine?
The first machine i will do a reset is the machine, my son (6 y) is playing around...
 

If the machine is at least on the network and you have some way of accessing the admin share (machine\C$) then you could copy the installer you need and use a psexec command to try and kick it off. In theory, anyway.

A reset machine has no open ports, no way to get in. So either you preconfigure your image, or you don't reset it (but rather repair it by doing an inplace upgrade).

All Windows computers have certain default ports left turned on.

If it's on the domain, it's easy to do with group policy.  If it's not on the domain, you can still do it, but you will need to set your computer to the same Workstation Group to be able to connect more easily.  You should also connect with an admin account that has the same name and password to make it easier.

https://www.how2shout.com/how-to/windows-firewall-allow-rdp-using-gui-powershell-command.html

reg add "\\remotecomputer\HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server" /v fDenyTSConnections /t REG_DWORD /d 0 /f

Then enable RDP through the firewall
netsh advfirewall firewall set rule group="remote desktop" new enable=Yes

It's been a while since I've had to do this, since I've been using Group Policy on Domain computers and VMs instead of standalone commands to set this up..

If someone has to touch it, you can also just enable RDP again.
I guess the question ist just, if you reset a device via RDP (means from outside, if you are NOT in front of the computer), how you can get controll again over it to finish the setup. 

@serialband
"All Windows computers have certain default ports left turned on." - which are? I doubt that. Please share what you know.

135, 445

No, definitely not these.