Modifications mean “tuning” the component to your taste and to work better with your other components. That means that any particular change may not be an improvement. Make sure that any change can be reversed. Damping horns is something easily done and reversed. Likewise, putting thin felt strips in the horn opening can be tried and reversed. If you are going with crossover modifications, make sure that the modifier gives you back the old parts so you or someone else can undo the change.
The biggest change, most probably for the better, would be to find a suitable tube amplifier. Take your time hearing alternatives. I know it is a matter of taste and system synergy, but, I find the MC 275 mentioned as a suggestion to be less than mediocre, particularly given the price. There are many low power tube amps that would work well with these speakers.