Power query function - loop for simple PQ functuin

Hi,

I have flat file (txt file) with  a lot of data.

I also have file with translation table of this txt file (e.g.: col 1-10-->XX, col 432-439-->YYY etc.)

I start with PQ to translate the txt file to normal table (with Text.Range duction)  soI can work with.

Then realized that there must be way to do it with "simple" function.

Can anyone please help with this kind of function?

I want to insert to the function:

• name of column
• start position
• lengnth of the string

and then place it in new column

Thanks in advanced,

Nir.