First thing to note is that all connecting flights within Europe will show as “economy plus” essentially because economy basic isn’t offered on those routings snd they will come with luggage inclusive but they don’t get the flexibility of eco plus point to point (such as same day change). I know it’s not your question but In other words they have exactly the same flexibility as a ba basic fare point to point - changeable for the same fee,

online you’ll only be able to change for the same origin and destination. Anything else will require calling and asking whether what you want is possible or not. Change of departure and/or destination is possible on most but not all tickets and change of country or departure is not always allowed on all fares though yes on most. And yes, ask for all changes at once - what is allowed in terms of stopovers etc will depend on your specific ticket conditions and will very likely incur a higher cost.