Changing a date stamp in Unix/linux within a file

Ok. I need to change ALL the date & hour stamps within a file. I have attached a sample file. I only want the date and times in column 1 (Jday) through column 7 (HR2) modified. I will then later modify the script in Perl. Unfortunately the Perl script requires a special module to be installed which I am having difficulty with. In Unix it is a simple thing to switch from UTC to local time but I need it to replace the current time stamp.  How would I do this? Again, the main date & time is column 1 (Jday) with the date and column (HR2). These need to be shifted back to local time HST which is always 10 hours earlier (no daylight savings time in Hawaii). So I could 1.  delete columns 2-5. 2. Read each row of data for columns Jday & HR2, then 3, change the date stamp & hour to local time.  For example, I look at three lines in the attached file,

12/03/2010 10 12 3 2 3 3 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00
12/03/2010 10 12 3 5 3 6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.00
12/03/2010 10 12 3 8 3 9 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

I would 1st delete the unwanted columns and it would look like this

12/03/2010  3 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00
12/03/2010  6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.00
12/03/2010  9 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

I would then change to time to look like this

12/02/2010  17 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00
12/02/2010  20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.00
12/02/2010  23 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

But this would be done for all lines of data in the file except the 1st line which names the columns
samplefile1.txt