Just create a calculated field;
if [race] = 'Maori' then 'Polynesian'
elseif [race]= 'Tongan' then Polynesian'
elseif [race]= 'White' then 'European'
Else 'the filter needs to be looked at'
The Else will error-trap anything else coming into the dataset, or if you have a 'Other' category I'd put them there.
Then in your viz, you simply use the calculated field instead of the original field.