previous good values calculations

Let's say I have x=[4.01 1004 1003 4.05 4.07 1899 1920] I want to change the big values according to the previous small value. For simplicity, let's say I want to apply a square and then add the big value. Thus, I'll have : y=[4.01 4.01*4.01+1004 4.01*4.01+1003 4.05 4.07 4.07*4.07+1889 4.07*4.07+1920 ].

If you want, let's say the small values are between 4 and 5 and the big ones between 1000 and 2000.

Thanks.