If you pick up the You're SPECIAL! book to gain +1 to any SPECIAL stat while a stat is already at 10, you normally won't be able to pick that stat. You will be forced to pick a stat that is at 9 or lower. So you normally can't use the book to go from 10 to 11 in a stat.
However I tested how the book works with stats that are affected by a de-buff because this would reportedly enable you to get the stat bonus even if the base stat is 10. Here's what I did and what happened:
- When I just took the book with 10 base intelligence and no int modifiers I could not pick Intelligence as the stat to increase.
- If I have 10 in Intelligence, drank some Whiskey to temporarily reduce my INT to 9 and then took the book, I was able to pick Intelligence to increase. When the duration of the Whiskey ended my total base INT was at 11.
So, what ways do we have to temporarily decrease each stat by at least 1 point in order for this to work with all stats? I would like to compile a list that at least covers each SPECIAL stat, without console commands.
Best Answer
One surefire way to get SPECIAL stat debuffs is to get addicted to a chem and go into withdrawal.
Below is a list of which chems produce a debuff to each special stat, and how much if not just -1. This is based on the screenshot Pierre-Luc Pineault put up in his excellent answer to "How many chem addictions are in Fallout 4?"
Something else relevant to note from that post, is that combination drugs like Bufftats addict you to the drug indicated by the prefix. Buffout, in the case of Bufftats.