I have a multi regressions as below and using esttab at the end to produce a publication-style report

Code:
reghdfe y x1 , a(firm year)
est sto m1


reghdfe y x1 x2 x3 , a(firm year)
est sto m2

reghdfe y x1 x2 x3 x4 , a(firm year)
est sto m3

esttab m1 m2 m3 m4 m5 using "directory\report.csv",star(* 0.1 ** 0.05 *** 0.01) ar2  title(" **y** ") mtitle("1" "2" "3" ) keep(x1 x2 x3 x4)
So, it will display the x1, x2 ,x3, x4 in the result table

However, instead of displaying x1, x2,x3, x4, I want to display them under other names called xx1, xx2, xx3,xxxx4 what I should do?

I read the esttab guide but cannot find the way out.