20070101 10.2317  79.1638   6.0  26.7  20.9   0.8  14.0  98.6
20070102 10.2317  79.1638   5.6  26.5  20.8   1.9  13.6  98.0
20070103 10.2317  79.1638   7.5  27.7  20.8   0.1  15.8  96.4
20070104 10.2317  79.1638   8.1  26.0  19.6   0.0  15.5  94.1

01/01/2007  10.2317   79.1638   6.0  26.7  20.9   0.8  14.0  98.6
02/01/2007  10.2317   79.1638   5.6  26.5  20.8   1.9  13.6  98.0
03/01/2007  10.2317   79.1638   7.5  27.7  20.8   0.1  15.8  96.4
04/01/2007  10.2317   79.1638   8.1  26.0  19.6   0.0  15.5  94.1

$ awk '{print $1}' filedate.txt
20070101
20070102
20070103
20070104

for i in $(awk '{print $1}' filedate.txt); do date -d "$i"  +%d/%m/%Y; done
01/01/2007
02/01/2007
03/01/2007
04/01/2007

for i in $(awk '{print $1}' filedate.txt); do dt=$(date -d "$i" +%d/%m/%Y) && awk '{$1=$dt}1' filedate.txt; done