AutoCAD Visual LISP / AutoLISP :: Changing Text In Attributed Block

I am trying to speed up some basic drafting of text revisions. In the P (plumbing) we call out the fixture units for a water pipe, along with the fixture units, the pipe size changes.
 
Is there any way to add numbers in an attributed block? (I have a lisp that works on text & mtext, but not attributes)

1.1. Example: Like if you have a block with two attributed text fields, the 1st field {x} is a number (fixture unit), and the 2nd field {y} is a number (pipe size).  I would want it to only add the 1st text fields. [If possible then change the 2nd text field according to a changeable chart. (see #2)]

1.1.1.   This is how the block looks like: x (y")
1.1.1.1.   x could be any number from 0.5 – 10,000 (only using 1 decimal place, and only as needed)
1.1.1.2.   y could be any number from the following list: ½, ¾, 1, 1¼, 1½, 2, 2½, 3, 3½, 4, 5, 6
 
Is there a way like in excel that you can set up a formula that will give a numerical result depending on other input? Like pipe size that change depending on the number of fixtures. There would need to be two different formula, one for hot and one for cold values (The value would be set at the beginning of the job; typically these values would not change later in the job). This could be separate text or if possible using the attributed block as described in #1.

2.1.    Example: Like if you have a block with two attributed text fields, the 1st field {x} is a number (fixture unit), and the 2nd field {y} is a number (pipe size).  I would want it to change the 2nd text fields according to the value in the 1st text field. If the value in {x} is 0.5 – 1.0, it would result in ½; 1.5 – 7.0 = ¾; 7.5 - 17 = 1; 17.5 – 36 = 1¼; ect.

2.2.    In excel it would be =IF(x)<1,"1/2",IF(x)<7,"3/4”,IF(x)<17,"1",…{all #’s in between} …IF(x)>5000,"6")))))