Partition internal iMac HD - Disk Permissions

This concerns an iMac 3.06 intel core 2 duo (about 2009) HD1 TB now active with Snow Leopard but with permissions that do not correct.***

Desire to erase and partition of (200GB) for Yosemite and 800GB partition for Snow Leopard within the internal drive

Will that create any conflict as the two programs are so very different?

if okay

I plan to erase and repartition the internal drive from an external FW hard drive

and the SL install DVD in an external DVD player instead of the internal DVD drive ?? any problems there???

===========

0-000-0-0-00-0

The iMac had SL but I upgraded to Yosemite. HOWEVER few functions were friendly so I will ONLY use Yosemite a few aspects -PREFERRING

TO do 90% of my activities IN Snow Leopard.

====

-------

[Yosemite HAS BEEN REMOVED to an external drive, and I reinstalled SL on the iMac, and then cloned appropriate SL files from a different Mac. However,

In checking verify permissions on the iMac I found about 100 "permissions vary" - and AFTER Permissions Verification is completed it still shows the same permissions varying... Puzzled, I checked the permissions on the Mac Mini from which I cloned SL and all it's files to the iMac and found that ALL the items are identical... apparently meaning they all are within SL on the Mini... So that's why the complete reinstall. to get it right.

After the the new SL install on the iMac I will re-install carefully selected programs from the Mini instead of cloning...so as to not prone errors.

Thoughts, ideas and comments or questions please