Is this question supposed to be different from your prior question? Having the frame professionally adjusted to 130mm would be best. Or doing the hub at some in between OLD (128mm?). and 'springing' the frame during wheel installation.

If this is just about reducing the left side spacers to get to 126mm, then see response #2. The second part of the response is about having to recenter/redish the wheel. This will change the right/left tension balance and may cause some problems with strength (depending on what the tensions are at 130mm).

A better approach, if possible, is to reduce the spacing on both the right and left side. 2mm on each side would be ideal, but 1mm R & 3mm left would at least be better that 4mm on the left.

What model hub are you working with? How many speeds are you running on the back?