Hi Chris
The answer as ever will be complex... but if the limiting factor is wing / 'g' then they would require a decrease in Max GW - the reason being that the wing now has a longer average 'arm' so an increased bending moment at the root. This could be 'mitigated' by reducing the 'g' limits accordingly, but the RV-6 Aeros (6g) weight is low enough as it is.
There can be an argument made that if an increase in weight is confined to the tip tanks themselves, they will provide an element of 'wing bending relief' - but how exactly that could be applied or offset the above decrease needs a lot of maths and complex limitations.
If the limiting factor is, say, the gear, then there would be no change.