How to make a random that guarantees the exchange of the original key presented in the variable?

Just a comment: In a previous question, I need to change the values, from column 0 to 1 or 1 to 0, depending on any value being parsed in the $myVar variable, the solution appended by a user here of stackoverflow was ideal:

$myWords=array(
    array('funny','sad'),
    array('fast','slow'),
    array('beautiful','ugly'),
    array('left','right'),
    array('5','five'),
    array('strong','weak')
);

// prepare values from $myWords for use with strtr()
$replacements=array_combine(array_column($myWords,0),array_column($myWords,1))+
              array_combine(array_column($myWords,1),array_column($myWords,0));
echo strtr($myVar,$replacements);

Inputs/Outputs:

   $myVar='I was beautiful and strong when I was 5 now I\'m ugly and weak';
//outputs: I was ugly and weak when I was five now I'm beautiful and strong

This Question:

But when in cases, do you see arrays with more than one option to make the switch? How to make the system do the exchange for any word among the multiple options, but without running the risk of doing "echo" with the key / word originally presented in $myVar that key / word that called the stock exchange action?

$myWords=array(
    array('funny','sad','very sad','hyper funny'),
    array('fast','slow','faster','very slow'),
    array('beautiful','Studious man','great beauty','very hardworking'),
);

$myVar = 'That man is really fast and very hardworking';

How to make the system choose among other options, but it exclude from the exchange or rand or mt_rand etc ..., the keys responsible for calling the action: fast, hardworking, so as not to run the risk of $myVar not be changed. output

$myVar = 'That man is really faster and Studious man';

The exit is with any other key, but the keys, fast and very hardworking, must leave the game, not participate in the rand, to ensure the exchange is made.

Thanks.