I'm sure what the purpose of this thread is about, but there are several ways of legally getting around an overload in a tight situation. However, not all options are open to all airlines, depending on their internal policy and, even more so, the willingness of the flight deck crew to accept the "creative book keeping" offered by the loadcontroller / dispatcher.
Regarding baggage weight. Handling agent I used to work for weighed in all baggage, but some of the airlines we handled would accept a standard weight per piece regardless. So, if you have an overload and find that the average weight per piece exceeds 13 kgs, simply mulitply the number of pieces by 13 to get an incorret but legal weight. That should get you parts of the way. If still overloaded, it is also for some airlines legal to presume that the carry-on baggage weight has been included in the scaled weight. Far fetched, but still legal. So multiply total pax count by 5 kgs and deduct from baggage weight. Now we're down to each pax having only 8 kgs of baggage with them, which is clearly a huge understatement but never the less legal.
These days I'm working with freighters only (thank god, no more pax !) and everything is scaled leaving no room to be creative with anything but fuelburn. Depending on whether you're restricted by TOW or LW you may try to convince the crew to burn a little extra on the taxi or trip fuel. But generally there's not a whole lot to be gained here.
Finally, before turning over a "creative" loadsheet to the crew, make sure they understand what has been done and why. After all, they are the ones taking your loadsheet to the skies and not you.
Why take these steps ? Because all loadsheets today are computer generated. In the good old days with paper and pen, you could "bend" a straight line to suit your needs or make some creative adjustments to the weights. All with the goodwill of the crew of course, but most crews are as interested as ground ops to get all pax / freight / mail onboard in order to generate a turnover for the company. It's business, not personal.
But the key here is to keep the flightcrew in the loop, so to speak. Failing to do so can have you facing a very irrate captain insisting on a loadsheet reflecting reality and nothing else. Keeping them informed, they'll understand the situation and will probably let you get away with quite a lot.
An instructor once told me (on another subject though) "It's allright to cheat, as long as you know what you're doing and what the implications are for all involved".
As to standard loadplans vs optimum trim. Well, I guess it's a fight over what's most important: Maybe the focus is on securing a tight turn-around and on-time performance, maybe it's on saving fuel, or maybe it's about maximizing the capacity in order to carry all bags / freight / mail etc. However, it's only during cruise that a tailheavy trim will save any fuel, so on a short sector with little cruise time, the fuel saved by a "perfect" trim may be wasted if you are late on the departure, or if you are leaving behind revenue earning payload.