Hi Miguel,
Yes, you are doing it correct. But keep in mind that the java script is case sensitive.
In your script, in the line function get_manaer_mskeyvalue (PaR)) you are passing the value as PaR
in the next like var managermskeyvalye = usIS_Get(2,Par);
It should be same in both the lines, either PaR or Par.
Correct it. It will work. Otherwise your approach correct.
All the best !!
~Krishna,