Reduction in Turnover under presumptive taxation

Respected Sir,

One of my friend filled his income tax wherein Turnover was  Shown as 42 Lakh for F.Y 15-16 now while filling 16-17 return i want to show income anyways higher than what is shown in 15-16 but by showing less turnover with high margin under 44AD 

I m doing this because my friend was not register with vat previously despite of showing such high turnover and now from F.y 17-18 i guess they are gonna track GST turnover along with income tax turnover i have taken his gst reg recently in december so i just meant if i m showing less turnover with high margin can bring trouble for me.

Under Sec 44 AD can i show net profit percentage different in different year i mean if i was showing 8% percent and all of sudden with less turnover more margin say 20% can invite problem for me ????