Yes, you can move the rim quite a bit left or right when lacing. Some times this is done to gain clearance or set the tire inline with the front.
On the XS650 the rim should be centered on the hub.
I don't have a 16 spoked rear to measure but I have a 18 spoked rear of my 75. It has the stock flanged alloy rim.
If you lay a straight edge on the hub were the brake plate goes so it hangs over the rim, mine measures 3/4 inch.
Flip it over and lay a straight edge on the sprocket it measures 2 3/16 inch.
Your16 rim may not be the same width as the alloy rim. My alloy rim is 2 3/4 inches wide. If your 16 inch rim is wider you will need to adjust those measurements. If you rim is say 3 1/2 inches wide, that's a difference of 3/4 inch. so you will need to subtract about half that from each measurement. 3/8 from the 3/4 is 3/8, 3/8 from the 2 3/16 is 1 15/16.
You get the idea.
Leo