Use regex with aliasSub to grab whole ( (.*) ) metric and change it - add desired text ( \1 last week ). E.g.
aliasByNode(timeShift(my.application.metric.$Continent.$DC.*, "7d"), 4, 5, 3)
should look like
aliasSub(aliasByNode(timeShift(my.application.metric.$Continent.$DC.*, "7d"), 4, 5, 3), "(.*)", "\1 last week")
https://stackoverflow.com/questions/38566535/combine-alias-functions