First download and load the '49ERSALL99' by M-Easy roster. This roster maxes put the attributes of all of the 49ers starters. It works especially well because I maxed out young players and rookies, not only currently older starters. So this roster will have superstars that will make your team go undefeated for the five years you will need to unlock this trophy. This roster also does what the NFL refuses to do and takes away all of the performance enhancing drugs away from the Seahawks, so their roster is very weak and will not pose a threat to you.
Once you have downloaded the 49ERSALL99 roster make sure you load it from the main menu. Go to Customize -> Manage Files -> Load and delete files -> Press once to move over to roster -> Press to select the 49ers roster -> The game will now warn you all progress will be lost, click yes to load.
Now go to the 'Play' tab in the main menu and start an offline connected franchise -> Create offline -> Choose "Import Custom Roster."
Use "Create Coach" and set him as a "Team Builder." While editing your coach under "offensive styles" and "defensive styles" turn the aggressiveness up to 70%
Choose the 49ers who will have a 98 adjusted overall roster (make sure you confirm the team is Overall 98). To efficiently unlock this trophy make sure you follow these settings:
Instant Starter: On
Salary Cap: Off
Difficulty: All Pro
Quarter Length: 7 Minutes
Accelerated Clock: On
Minimum Play Clock Time: 20
Game Speed: Normal
Player Progression Frequency: Every four weeks
Coach Firing: Off
Game Play Tuning: Yes
Injuries: Off
Pre Existing Injury: Off
Trade Deadline: Off
Trade Type: Enable All
Dont worry about Team Settings unless you are going to actually be playing in the game
CPU Settings:
Fill Roster: On
Re-Sign Players: On
Progress Players: On
Sign Offseason Free Agents: On
Simulate Game Prep Activities: On
Now once you are in the main menu select "advance week" and simulate the season. You should go 16-0 and win the super bowl every year, I did. But to be on the safe side you may want to simulate up until the Super Bowl, save and then simulate the big game to make sure you win it. Once you have won five Super Bowls this trophy will unlock. I've test this method twice and have won the Super Bowl after 5 seasons both times so you are safe to choose "simulate 10 years" and stop after the 5th year.