I think the evidence of excess compression at the mizzen is not very unusual but a worse than normal example judging by the photos. As you point out it is probably not a problem though. The angled design at that time between the mast foot and the compression post (under the cockpit seat) would put forward pressure at that point and buckle the seat if too much compression is put on. As the mainmast has it's own backstay and the mizzen is small, I can't see an advantage of making the mizzen rig very tight unless you a big user of the mizzen staysail, so I would er on the side of caution and loosen off a couple of turns on the turnbuckles. Obviously check the area under the seat as much as possible, and the fastenings. I can't imagine there would be any problem below that. Keep an eye on it getting any worst though. I don't think slackening the rig will put the seat back where it used to be.
It seems unlikely you could have forced the bulkhead under the mainmast downwards if all your woodwork is in good condition. Hopefully there is a simpler explanation for the forward bulkhead door like hinges or something.
If you can see the bottom of the mast compression post for the main mast I would check it for any sign of rot. It should be sheathed in fibreglass so may be hard to tell. I have not heard of it being a problem but it can sit in freshwater a lot if water is left in the sump where the sounder transducer and seacock for the forward head is. This is basically your worst case scenario but even so I can't imagine you could force this bulkhead out of alignment unless the shrouds were really massively overtightened because of the fully tabbed in main bulkhead giving structural support.
The Maramu does have a simple rig and I can't imagine the tuning is that critical. I've had a few yachts and done a few ocean crossings including in a Sparkman and Stephen 39 with a fancy tall pre-bent mast which I re-rigged myself and sailed from East Africa to England including encountering some faily rough weather going up the Red Sea, in the Med and off Portugal, all without the rig falling down;) If if you don't use a lot of force and/or big tools you would be hard pressed to deform your boat by a small tightening of the rig. Taking a huge spanner to get more leverage, or really putting weight into turning the turnbuckles is different.
I would try not to loose too much sleep over it at this stage..even if the rig has been over-tightened boats can flex and have some spring to return to their original shape rather than just bending!....Before I did lose sleep, I would check the bulkhead door accurately then slacken the mainmast rigging (write down the number of turns for if you want to put it back) and then check the door again. You may have a bit of flex and it show up rather than any permanent deformation. As for what to do about trying to improve it, you can check your rake with a plumb line. My mast is basically straight. I don't see a problem with a little aft bend but I personally would keep the rig so that it is straight and true to the centre-line (checked with the plumb line from the mainsail halyard sheeve) and have the rig so there is a slight slack (but no floppiness) on the leaward rigging when under moderate sail and healing. If adjusting the rigging do a little at a time and always note numbers of turns. Tack to do the same on the otherside. Check the mast is still in line and make sure not to overtighten. Adjust the stays to make sure the mast is straight and has no "S' bend. Obviously easier on the earlier Maramu with a single spreader otherwise do that same with adjusting the intemediates to avoid an "S" shape in the mast. As for fore and aft, you obviously want the rig tight enough to have little sag in the forestay and headsail luff. So you need the back-stay tight enough to have correct tension in the forestay without the mast bending forwards. If your forestay is rock solid with no bowing under a decent sail it is probably too tight - unless you are a Volvo 70:)
Lastly please note this response is my own personal opinion and I am not a rigger. I am replying as you have asked for opinion from a Maramu owner and according to what you have said the rig was set up by a rigger and then only tightened 1 1/2 turns by yourself (a couple of mm at the most) so it sounds like you may be unduly worried. I have an early Maramu with a non furling mainsail and a single spreader Isomat mast.
John Maramu #91 1981 Popeye (located in Port Douglas the home of Peter Grieg - probably the best rigger on the East coast of Australia who does also sometimes travel to Townsville so maybe did your boat?)