"strictly" changes the meaning of the sentence. it suggests that there are "strict" and "not so strict" interpretations of the chess rules, and that if you're not so strict, the move is OK.
but promoting to the other color is not allowed, even under "not so strict" interpretations of the rules of chess.
an example of things that may be permitted in "not so strict" chess: taking back your move, not moving a piece even though you touched it, talking to the other player, agreeing to play on even though you've had a threefold repetition.
If my opponent would use that move, I would probably consider it as a severe case of rule of cool. ( But this may be the reason, that I prefer RPGs to chess. )
I mean really, the rules are the rules, and there is no ambiguity. So a "strict reading of the rules" is the same thing as a "reading of the rules." Because, as you say, there is no such thing as a reading of the rules that violates the rules and is thus merely "less strict."
For example, under the rules, not moving a piece you touched and promoting to the other color are the same: illegal.
The examples you are giving are simply cases where the other player is likely to let you break the rules if it's a very casual game.
So again, having "strictly" in the sentence is, technically, purely redundant.
It's a dumb thing to say, but then again, it probably made the piece more suspenseful and thus more fun to read.
You seem to imply that all rules are equally as important as one another, while I would say they are not. For example, in a casual game of chess, most would be okay with some of the aforementioned deviations, like taking back a move. I do not think most would accept it if you started moving your pawns around like queens.
It gives the sentence a nuance that suggests ambiguity, as if prohibition of this move requires some particularly "strict" reading of the rules. I agree that makes the sentence weaker, and given the gravity of the sentence, makes the article seem somewhat amateur.
