Question

Can Man Alter Mars Environment

Answer 1

Theoretically yes
if we where able to grow sustainable plants that can live on mars nutrient deficient soil we could change mars environment
we could burn hydrogen to produce water or synthesise it  by other methods to produce pure clear water for mars 
the plants planted on mars could change its atmosphere composition 
if we where to use giant solar powered heaters we could melt the ice on mars and turn it into water vapour to trap the heat into its atmosphere 
certain animal species could be grown on mars to live there 
so yes its theoretical possible to alter mars environment 
hope that helps