Although the most interesting effect of SCP-XXXA and SCP-XXXB
Wonky grammar. Start the sentence differently.
The idea? A genderswap SCP? I won't be surprised if it's been done before. Execution of it doesn't contain any rage-starting mistakes yet, but the general idea toes the line between silly and serious. Also, most importantly, it isn't scary. At most, it's interesting as a cliched idea done right, but expect a bit of flak incoming for this.
As for improving it? Think of some consequences, but don't throw them in just to be there. Think of WHY the Foundation would want to contain this, or if you want to keep it at Safe, think of how it makes this different from any other sex-change potion one could find in some fantasy setting etc. Right now, it's not particularly novel.
Last addendum not necessary, goes down the path of "Note from O5 stating that no more hilarity ensues antics are to be done with this SCP, cos people working in the Foundation are idiots." The non-explanation of these shenanigans can be seen, in my opinion, as both a blessing and a curse, because on one hand, you were too lazy to think of a situation to explain it, one the other hand, thank god I didn't have to read a "hilarious" tale about genderswapping.