USE "OBSOLETE" TO KEEP CONTROL: The simplest way is to create specialist designs and immediately obsolete them in the right design form column after ordering the number you want and before unpausing. AI won't use obsolete designs. No retrofit will occur except when you go and unobsolete them and either order builds and individual retrofits or let the AI pick them as purchase options or for refit.
The way I use this, Explorer spy (scanner) ships, pinning (hyperdeny/tractor) destroyers, fast command cruisers, monitors, special super-fortified mining stations or bases, missile boats, assault (dual role) transports, etc. all may spend time in "obsolete" status while the standard fighting ships are left non-obsolete for periodic builds, unless they are lagging behind enough to discontinue orders but design/build of better versions is premature (e.g., waiting for an important upgrade).
RETROFIT STRATEGY AND DESIGN CYCLES: Some people say YES to all retrofit suggestions or auto-retrofit, but it costs time and money and doesn't feel right to me to appropriate the funds and stand down warships unless the improvements are worth the time, money and resources at that time. Some ships don't need upgrades to continue to serve their purpose effectively.
Often it seems reasonable to wait for peace or a new component before rolling out a new design. For an empire well under way a wave of fresh designs might roll out every 2 to 4 years after a research or military stimulus, with a lot of following rolling retrofits - unless at peace. when it is safe to send whole fleets to the space docks.
Incremental redesign for new purchases of a ship type can be more often as a new "mark". I use design year or function codes in ship names for easy recognition and since there is no "notes" field for designs to explain their purpose.
It might be interesting to open a "ship function" topic just to discuss different concepts that people use.
< Message edited by Keston -- 7/29/2014 4:47:50 AM >