I presume there is a reason you want to do this, such as to mount a dodger.
Generally, the further aft the Traveler/Boom Bail is the lighter the load on the Main Sheet will be relative to Leach tension. (torque = force x distance). On the Islander 27 the Traveler is already relatively far forwards (approx. 50%). Moving it 7" probably will not be noticeable.
Having an offset between the Traveler and the Boom Bail will add a bit more compression load to the Gooseneck. Unless you do a lot of racing or sail with the Sheet in hard in heavy wind then you don't need to be too concerned in this respect.