Hi, JeffCr!
First of all welcome to Chandoo's website Excel forums. Thank you for your joining us and glad to have you here.
As a starting point I'd recommend you to read the green sticky topics at this forums main page. There you'll find general guidelines about how this site and community operates (introducing yourself, posting files, netiquette rules, and so on).
Among them you're prompted to perform searches within this site before posting, because maybe your question had been answered yet.
Feel free to play with different keywords so as to be led thru a wide variety of articles and posts, and if you don't find anything that solves your problem or guides you towards a solution, you'll always be welcome back here. Tell us what you've done, consider uploading a sample file as recommended, and somebody surely will read your post and help you.
And about questions in general...
If you haven't performed yet the search herein, try going to the topmost right zone of this page (Custom Search), type the keywords used in Tags field when creating the topic or other proper words and press Search button. You'd retrieve many links from this website, like the following one(s) -if any posted below-, maybe you find useful information and even the solution. If not please advise so as people who read it could get back to you as soon as possible.
And about this question in particular...
I don't know if I understood correctly your question but let me give an example:
a) Column A, any data
A2:A10 : 1,2,-1,0,3,...
b) Column B, your 1st posted formula
B2:B10 : =IF(A2<0,"40=1","40-2")
c) Column C, your 2nd new formula (e.g., add or subtract column A value to/from 1000)
C2:C10 : =IF(B2="40-1",1000+A2,SI(B2="40-2",1000-A2,1000))
Regarding the topic title, there's no difference between testing the result of a formula and the value of a cell, you always refer to the cell (A2, B2,...) and Excel evaluates if retrieves directly the contained value of the result of the formula or expression.
If that's not what you wanted then consider uploading a sample file (including manual examples of desired output if applicable), it'd be very useful for those who read this and might be able to help you. Thank you. Give a look at the green sticky posts at this forums main page for uploading guidelines.
Regards!