And how may I ask do you know what cichlids carry the trait you are speaking of. Cichlids are called tropical fish for some reason. DUH! Probably because they come from tropical waters.
What part of 'possibly' did you not understand?
Cichlids may or may not have any preadaptations to the cold, but that doesn't mean over many generations they don't accumulate genetic elements that would allow them to survive in the cold. Same as any organism really, that's how we get all these organisms living in all sorts of environment. Most african cichlids require a (relatively) high pH but Red Forest Jewels require a (relatively) low pH. What, did you think RFJs just dropped out of the sky as is or something? Obviously not, at some point either the RFJ split from the rest and adapted to a lower pH lifestyle, or most Africans had to adapt to a higher pH lifestyle, or both had to adapt from an original different pH lifestyle. Whatever the case, at least one species had to evolve to adapt to the pH of their environment. If cichlids can evolve to survive in lower/higher pH, then they can evolve to adapt to colder temps, or other environmental factors that they are not used to.
Mutations occur all the time, tweaking genes and other genetic elements constantly, producing new varieties of genotypes. By subjecting a species to colder and colder temperatures and selecting the ones that adapt best to breed on, one will be selecting for the genetic element(s) that confers cold resistance, whether they are already there, or eventually will develope through mutations.
Of course, it is
possible that it may never work, hence why I wrote 'possible', but chances actually that it would work, over many generations. It will take a lot of work, but it is entirely possible.
