Unless I'm mistaken it's fairly easy with conditional formatting, no VBA required. If you think ahead and know that for example, column A contains names, and column B contains their sales figures, and you want to subtotal for Sum at each change in name, that means you know that "Total" will be the five right-most characters in column A, where in the corresponding cell in column B will be the subtotaled sales amounts.
Therefore, assuming your field header row is row 1, select A1, press Ctrl+Shift+*(8) to select the current region, with A1 as the active cell.
Now from the worksheet menu click Format > Conditional Formatting, select Formula Is from the drop-down, and enter
=RIGHT($A1,5)="Total"
Note the $ character in front of column A in that formula.
Click the Format button, select the Font tab, choose Bold in the Font style pane (because you said you wanted the subtotaled rows to be Bold), click OK, then OK.
Finally, do the subtotal and your sheet will be conditionally formatted for bolded cells in the subtotal rows.