Transferring user account data on Migration Assistant without deleting existing files

Rocketship01 wrote:

I have seen that guide before, but the problem is I messed that up, by opening the new MacBook in the store when the sales rep showed it to me, and already had set up the new MacBook before using Migration Assistant and creating a user profile with my name as before with my Apple account. I already have work on it, and I do not want to lose it by overwriting the new one, or having to go back and forth between the two to get anything old.

Is there any way, possibly, to transfer the files over to the new user profile from one created by copying the old computer? Then deleting that user profile created by MA because it's redundant? Otherwise I'll use the internal hard drives. I still really wish they'd allow simple Thunderbolt connection without MA.

I wouldn't say that you messed up -- Apple's guidance (including that sales rep, who should have explained to you the best way to proceed) could be clearer on this.

You do have several options, and I think all will work, some will be easier for you than others:

• Use Target Disk mode and manually copy files from the old computer to the new one. The main downside of this method is that it might take some time if you have many files. But you have Thunderbolt 3 on the old Mac which can be up to 40 Gbps; in practice you will get less than that, but let's say you get 20 Gbps, which is about 2 GB/s. Copying 1 TB would take 1000/2 =500 seconds, about 10 minutes. To be conservative, say 20 minutes, which is not bad at all.
• Make a "clone" type backup of your entire old computer to a fast SSD with Thunderbolt 3 or a fast USB-C interface. Then connect the SSD to the new computer and again, manually copy what you want from the old computer. It's a good thing to have such a backup anyway, so you get a bonus here. Examples of "cloning" utilities include SuperDuper and Carbon Copy Cloner (there are others as well). Some of them may have a free version without all the advanced features.
• Run Migration Assistant, have it create a new user, do not overwrite the user you already created on the new Mac. Then you will need to modify user permissions so that new user containing the migrated files can be accessed by the user you have already created on the new Mac. This can be tricky, and given that either of the previous 2 options will work well, I would not go this route.
• I would recommend against wireless connections for these transfers. They could be 10 times slower or more and more prone to errors.
• I would recommend against using cloud storage to move the files because non-Apple cloud services (like Dropbox) don't always preserve the unique structure of specialized files like Photos libraries. As for Apple's iCloud, I think it will become confused between your "old" Documents folder and the "new" one, I don't think cloud services will accomplish what you want here. Also cloud storage transfers are limited by the speed of your internet connection.

If I were you, I would go with the external disk/clone method described above.