A little patience, please. A lot of the regulars, including me, are usually asleep when you posted.
If all the numbers are preceeded by the tab and have no fracrions, then (?<=\t)\d+ should work, but I really don't know what numbers you want to change besides the first number...
I want the fractions only to change to my new character style
but not the fractions in the parenthesis
Just the fraction, or the whole numbers too? Is there ever any text between the parenthesis and the first digit?
And are these "real" fractions (single glyphs for the whole fraction included in the font) or fractions made by typing digits and the slash?
just the fractions
the real fractions - not man made with slash
Off the top of my head the only way I can think of to do this is to create a class with all the fraction characters you will be using and use a negative look-behind, like this: (?<!\(\d*)[½¼¾⅓⅔⅛⅜⅝⅞]
I created that class by making a text frame in ID, then double-clicking the fraction glyphs in the Glyphs panel to enter them in the frame, then copied and pasted them between the brackets for the class in my GREP.
OK, that displayed badly....
Should be all together.
This will find any fraction in the list that was entered as a glyph (it will NOT find typed fractions to which the OpenType Fractions property is assigned) and also that is not preceeded by an open parenthesis and 0 or more digits.