It depends by how much. An inch would be ok, any thing more would damage or kill it. You could raise the border but build a wooden a 'box' around the trunk leaving plenty of room on the inside to allow air, water and of course growth to continue as normal. How deep are you planning to raise it?

you could build or get built a kind of reverse planter bye building a brick wall round your tree to the hight you want your soil then there will be know problems . it mite be better to not cement the bricks as the roots will break it . you could use natural stone or perhaps cut a strong bucket bucket down to the right hight and cut down one side and put a few bricks inside to stop the soil pushing it in . then hide it with some choice planting etc . its never good to put soil above wear its been before .

Thanks for the information. It's what I thought and just needed confirmation. I will certainly use one of these methods.

your more than welcome kjak .