如何在linux中重命名列？

I have a table like this

我有一张这样的桌子

 bedGraph  chrom=chr1 chr1:0-000
    1000    0
    2000    0
    3000    0.003802
    4000    0.046175
 bedGraph  chrom=chr2 chr2:5000-6000
    5000    0.103756
    6000    0.161337

 EXPECTED RESULTS

bedGraph  chrom=chr1 rep
    1000    0
    2000    0
    3000    0.003802
    4000    0.046175
 bedGraph  chrom=chr2 rep
    5000    0.103756
    6000    0.161337
 bedGra