If your company procedures in specific instances specifically require a force tune on the RADNAV page (MAN/MAN etc) - of course comply. However as a technique, I would discourage it.
Auto tuning relieves pilot work load and ensures "agreement" between the pilots and the airplane on exactly what approach is to be flown. Our company procedures have us clear out any manually tuned NAV aids used during departure at 18,000. (ie KORD climb restrictions, etc.) Manually tuned NAVAIDS prevent auto tuning.
If one were to leave a manually tuned ILS freq in the RADNAV page (back up to departure procedure say), cockpit confusion would result, at least for a bit, when the MCDU "RWY/LS MISMATCH" message appeared. Or as others have posted, a late runway change - not only would one have to install and brief a new approach you would have to retune the RADNAV page - why do that to yourself? The Thales engineers seem to me to be a pretty sharp group, I would go with what they came up with.