SQL change value for result set, but don't update

I would like to select a data set and depending on the criteria, I would like to change the value of specific cells, but I don't want to change the original data, just specifically what is seen in the resultant set.

I.E.  if my source=Code1, then in the result set, I would like it to show "Changed Code", but I do not want to update the source table.

How can I accomplish this?  I am trying to work with CASE setting criteria.

I have tried:

case when source='Code1' then source='Changed Code' else null end

but it doesn't work

Suggestions?