Well, concernng automation, the only way I know is recording a macro. I can record a simple macro that will start from the left end of a text string, move a certain number of spaces to the right, then select a certain number of characters, apply the bold font to them, and then move down to the next row and stop. This could be rapidly executed on multiple rows by just holding Ctrl plus the key assigned to the macro.
Now, this only makes sense where you want to select chararacters from the same character location or position within each row. So, I doubt that is what you want.
Someone proficient in VBScript may be able to develop something much more sophisticated.
Let me know if you want more info on the macro.