Is it possible to upload Performances without Rig Manager?

Probably, but, I have never tried it. I used to do something similar with large numbers of Rigs before Rig Manger was available, so it should .

The biggest danger doing this with Performances may be adding the new ones without losing your existing Performances. So, make a backup before you try anything.

So, you should make a backup file, to use in case things go wrong. (this is your unofficial reminder!)

Then, make a second backup file,with a different name, to use to add the Performances.

Un-Rar your second backup file (this is another unofficial reminder to make more than backup file!)

There is a Performances folder in a KPA backup file.

In the Performances folder, the Performances have simple names, presumably denoting their Bank locations:
1.kipf, 2.kipf, 3.kipf, etc.

The safest approach would likely be to add the additional Performances using numbers higher than the largest numbered Performance already in the KPA.

So, rename the Performances on your MAC before adding them to the backup file.

Add the additional Performances.

Re-Rar the backup file - save it with a new name, so you will know it has the added Performances in it.

Put the updated backup file on the USB, and load the backup onto the KPA.

What do you mean by old? old OS version? old hardware?

If you really don't want to update your MAC OS, which may make sense in certain situations, consider getting Parallels and a cheap OEM Win7 or Win8 License Key to be able to run RigManager.
You can install the Virtual Machine on an external harddrive, if you don't want to clogg your main drive.

You may find a few discussions in regard to your question when you use the search, but to be honest - you can do as Paul explained but managing performances without Rig Manager is a pita. The Kemper deserves better - and you do too!