Oh, you want to edit it yourself? I cannot remember the name of the parameter in the .dat files, but there is a .dat file reference on the forum somewhere that should tell you all about the various parameters for signalboxes. How to compile the pakset once you have made your changes is already explained in the tutorial on how to make additional liveries: the principle is the same.
In terms of the broader question of how the signal limits ought to be calibrated, it is not much use thinking about how many signals that an actual signalbox of the relevant type would control, as a real signalbox would control level crossing signals, shunting signals, repeaters, yard signals and many other things that are not directly simulated in Simutrans. The signal limit is instead intended to be proxy for an overall limit on scope of network that a signalbox can handle. This is much easier to calibrate for smaller signalboxes than larger signalboxes.
Thus, whilst it does not make sense to abolish the limit entirely as it has a specific purpose, if there be some reason to believe that the limit is too low and that some other specific higher number would better reflect how these sorts of signalling centres are used in reality, then I am certainly amenable to amending the limit - but cannot sensibly consider that without more detailed information as to the reason that the current limit of 175 signals (which is a lot for Simutrans) is too low. For example, if a real ERTMS signalling centre covers network of scope and complexity that is considerably greater than that which can be covered by one in game, then it would be reasonable in those circumstances to amend the signal limit to allow an ERTMS centre to control the same scope of network as it would be able to control in reality.
If anyone has any clear data on this, that would be most helpful. Otherwise, you might want to consider either using more ERTMS centres or an ERTMS centre combined with some smaller signalling facilities.
