iTunes 12.9 > 12.8

Hi,

Is it possible to take iTunes 12.9 back to iTunes 12.8.

I want to take my iMac back to High Sierra but my iTunes library won't work. I have iTunes running on an external HDD as it is 2.5tb in size and its not practical to have that on the actual machine.

I am finding this machine the poorest iMac I have ever had:

iMac (21.5-inch, Late 2015)

2.8 GHz Intel Core i5

8 GB 1867 MHz DDR3

Intel Iris Pro Graphics 6200 1536 MB

I have put a 500gb ssd on but externally as I did not want to open the machine. Even then I don't think it will make a lot of difference.

I hope someone can help...

Thank you in advance....