If you're doing railings with plastic, tiny drops of solvent cement at the bend points allows for smooth corners, etc. Practice on some non critical parts first, though - the amount of glue needed varies with the thickness of the parts, the type of plastic they are made of and the formula of the cement. So, too many variables to sort without first doing a bit of experimentation. For example, some cements will allow you to bend right away while others may take a few seconds to soften the plastic so it won't snap while bending.
If you think this sounds tricky, using hot water with such small cross section parts will be even more so. Perhaps, if using heat, try an hair dryer instead. On low heat!
If you can swing it, Keith has the best suggestion. Gold Medal Models has an excellent photo-etch (PE) brass set for the Titanic, in fact several. Includes a whole lot more than just railings!
If you are asking this because you are using brass PE, hot water will have no effect. You need 'flame hot' to anneal the metal (heat red-hot then allow to cool slowly) to soften the brass significantly. I expect if you Google 'annealing brass PE' you'll find a ton of videos on the technique.
Good luck!
Regards, Robert