In theory if you can keep dust off the platters, then you can swap the platters DIY.
It is a last resort, you must not jog the platters whilst putting the heads back in place. Original disks used magnetic influence/springs at the head arms to keep them far enough away, recent tech. uses air pockets. You are not likely to get more than a couple of hours use once you have broken the seal on a disk.
If the heads are stuck, the more successful way of recovery is thermal shock.
Wrap the disk in a food plastic bag. Put it in a freezer for 8+ hours.
Then take it out, tap it on the side of a desk sharply to loosen the heads, then put it in a machine. You will have until the disk warms up again to recover your data.
Cheap data recovery units will usually do similar actions as the above, and also try to access the disk directly putting pwm onto the drive motor and reading the values off of the heads without the use of the controller card on the drive.
The more expensive/proper labs, will break the vacuum seal, and will try and read the raw data from the platters. Then reconstruct it. Proper labs will deal with raid drives, whereas a cheaper lab will only deal with what can be seen as real data on the disk.
