Originally Posted by andybg40
Can I flash an LTE-A version with UK firmware?
There isn't a lot of reliable information about your model so there is no authorative answer.
Most will say that it's risky and not recommended to flash a firmware from another variant. As well, you don't simply have a different variant of the 801 Snapdragon based S5. You have a derivative model, with a different processor (805), screen resolution, et cetera. Strongly arguing that it is highly unlikely to work and would likely brick your phone.
The best you might hope for is someone alleging that they were able to do so. And then you'd still need to estimate the credibility of such a report.
If you have root and a custom recovery installed, you could remove much of the risk by trying a 900F based custom ROM, e.g. the Phoenix ROM, rather than flash stock 900F firmware. All in all though, it's an improbable fit.