Add specific text to columns in file by sed

What is the proper syntax to add specific text to a column in a file? Both the input and output below are tab-delineated. What if there are multiple text/fields, such as /CP&/2 /CM&/3 /AA&/4 Thank you :).

 sed 's/[^\\t]*/Index&/1' del.txt.hg19_multianno.txt > matrix.del.txt 

Could you please provide sample input and expected output?

In the attached .zip the text file is the input and the .xls is the desired output.
The green highlight comes from the text fie and will have S1 - AP1 as row headers. It will also have data in those columns ... A1 - R1 (headers only) and AQ1-AX1 (headers only). No data is needed for those columns (only the headers). I have a SQL import that is expecting all those columns in one file.

Code:
Index Chromosome ... Amino Acid Change Chr Start ... clinvarsubmit clinvarreference HP SPLICE ... Sanger References

So, the text in bold is added to the text file and a new file with the combined is saved in the path. Thank you

This is the same problem that you asked in your other thread:

where you had posted a Perl program to solve this problem.

Why two threads with different programs (Perl and sed) for the same problem?

I was just curious as to how sed would handle this. I am just trying to learn shell scripting as it is very useful in the sciences. Thank you :).