Unfortunately, it is not possible to embed font/size changes within an Excel formula. Formulas are used to calculate values and cannot contain formatting instructions. However, there are a few workarounds that you can use to achieve a similar result.

One option is to use the CONCATENATE function to combine the text from multiple cells into one cell, and then apply the formatting to the combined text. Here's how you can do it:

1. In a new cell, enter the CONCATENATE function, followed by the cell references of the cells you want to combine. For example, if you want to combine the text from cells A1, B1, and C1, you would enter the following formula:
   Code:

   =CONCATENATE(A1,B1,C1)

2. Once you have the combined text in the new cell, you can select the portion of text that you want to format differently and change the font, size, color, etc.

Another option is to use conditional formatting to apply different formatting to different parts of the text based on certain criteria. For example, you could use conditional formatting to apply a larger font size to the first word in a cell and a smaller font size to the rest of the words. Here's how you can do it:

1. Select the cell or range of cells that you want to format.
   
2. Click on the "Conditional Formatting" button in the "Home" tab of the ribbon.
   
3. Select "New Rule" from the dropdown menu.
   
4. In the "New Formatting Rule" dialog box, select "Use a formula to determine which cells to format".
   
5. In the "Format values where this formula is true" field, enter a formula that will identify the first word in the cell. For example, if the first word is always separated from the rest of the text by a space, you could use the following formula:
   Code:

   =LEFT(A1,FIND(" ",A1)-1)=A1

6. Click on the "Format" button and select the font size and any other formatting options that you want to apply to the first word.
   
7. Click "OK" to close the "Format Cells" dialog box.
   
8. Click "OK" again to close the "New Formatting Rule" dialog box.
   
9. Repeat steps 3-8, but this time enter a formula that will identify the rest of the text in the cell. For example, you could use the following formula:
   Code:

   =LEFT(A1,FIND(" ",A1)-1)<A1

10. Click on the "Format" button and select the font size and any other formatting options that you want to apply to the rest of the text.
    
11. Click "OK" to close the "Format Cells" dialog box.

Now, the first word in each cell will be formatted with the larger font size, and the rest of the text will be formatted with the smaller font size.