Sugar in tea better if put after boiling
Yes, it would taste different-
Sugar chrystals are made of sucrose saccharose(glucose combined with fructose), if you boil sugar with an acid (milk is slightly acidic[ph 6.5-7]) your sugar splits into its monomers-fructose and glucose(invert-sugar). 
Fructose fits into your taste receptors better than sucrose or fructose causing it to taste sweeter(1.73 x sweeter).