After takeoff, pilots (plts) had difficulty retracting landing gear (LG), and manually bypassed LG anti-retraction system to retract gear. While climbing, they realized cabin pressurization (CP) and takeoff warning (TW) systems were still in ground mode. There was evidence the nosegear shock strut was underserviced/underinflated for cold/winter weather operation; and the strut did not extend sufficiently to actuate the ground shift mechanism, to release the landing gear lever anti-retraction mechanism, and to shift aircraft (acft) systems to flight mode. Using quick reference handbook (QRH) procedures, plts pulled Ground Control Relay circuit breakers (C/Bs), then noted CP and TW began operating in flight (flt) mode. En route, the flt was uneventful. Plts decided to reset C/Bs just before touchdown. They made a normal approach to runway, and on short final approach, Captain reset C/Bs. At that time, ground spoilers activated, and acft descended rapidly, striking ground tail first in runway approach light area. Abnormal procedure in QRH stated 'GROUND CONTROL RELAY C/Bs (if pulled) . . . RESET . . . .' This was listed in 'Approach and Landing' section of procedure. Acft operating manual (AOM) stated 'Reset Ground Control Relay circuit breakers during taxi . . . .' Plts stated they had not referenced AOM, nor did they notify company of in-flight irregularity. (See: NTSB/AAR-96/07 for detailed info)