[Dinadon]

Originally Posted by Icelander

They are, effectively, cross-trained to the extent that they can do both jobs.

Why is it impossible to keep a regiment that can function either as Bowmen (in case of a siege or when defending someting) or as Heavy Infantry (during battles where they want to close)? The tactical flexibility is worth something and though a larger country might gain more benefit from specialising, this is specifically a small city state that has comparatively few men, but has historically been very rich for its size.

It isn't impossible, it's impractical. Taking the time to train a group of men to do two things could also be spent training both halves of the group twice as well at one thing. On the march, you only want to carry the stuff you'll be using in battle that day, the same can be said in a siege or at a guard post. You can't know in advance if you'll need archers or infantry, so it's better to have half infantry and half archers. Plus, bowmen work best when they have infantry in front of them to prevent them being overrun. I am slightly surprised you haven't actually got dedicated archer units, not even as levies.
If you really want people who can perform in both roles adequetly, buy bowmen with the Hero modifer and have it change their TS to equal Heavy Infantry. A realistic approach would be Bowmen with both Good Training and Good Equipment, but they will never be as good as similiarly modified Heavy Infantry. In either case, it just becomes a feature that they won't add to fire superiority in some battles. And don't forget to change the elements name and to modify the description as appropiate.

In fact, I think that a lot of historical units would be capable of switching between two roles depending on the tactical situation. British infantry battalion had a company of Light Infantry that was equipped and trained to stand in the line of battle as normal Line Infantry during intense battles, but was also capable of serving as Skirmishers.

Those were simply men picked from the rest of the battalion for their intelligence and ability to function outside of the battleline, but that didn't mean they suddenly lost the ability to perform as the Line Infantry they had been trained as.

There's nothing to say how your troops form up on the battle line. If your battle stratergy calls for your Skirmishers to form up with your Line Infantry, there's nothing stopping you. However, training them as Skirmishers detracts from time that could be spent training them as pure Line Infantry, and may also mean that they travel lighter. If your Skirmishers aren't any less effective (in terms of TS), then you should be applying Quality and Equipment mods so they do match up with your Line Infantry.

I think that an ability representing such capability (Multirole +20% or +25%) is necessary. It would take a round or so to switch roles and the TS might be different in each of them (in fact, it nearly certainly would be).

To which I would just say this is covered by the training and hero modifiers. Changing TS normally has no effect after the battle has started. Even if you are going to track the changes, if the overall effect is similar to just applying improved training to the weaker of the two types then do the simplier effect.