AE's safe areas are broadcast spec, but hardly anyone uses the safe areas any more for anything but legal disclaimers. As far as I know there's no way to change the template. You could always create your own guide layer.
I've been in television and film production for more than 40 years. Broadcast spec as always been action safe 95% and title safe 90%. LCD and Plasma displays don't overscan as much as CRT's Projectors also don't overscan very much. That's why most folks only strictly follow the 90% rule for legal disclaimers. Most lower third crawls extend into the safe action and beyond. I've never heard of a spec that didn't have equal values for horizontal and vertical. AE's safe area template works for both square and non square PAR's. It just looks wrong in non square uncorrected.
If you are talking safe action and safe title for a 4:3 broadcast of a HD (widescreen) image all bets are off. I'm on a cable network at home that uses different crops for re-broadcasts of the same program on different channels. MASH is cropped top and bottom on one network so it looks widesacreen and shown 4:3 on the other with black pillars. I've even seen it shown 4:3 but scaled even more so that there's black all around the picture. Commercials are all over the place on different channels. It's all kind of a mess.
AE safe action safe title:
Guide layer created with two masks and stroke. Both for 16X9
British, Australian and NZ Broadcasters do require all graphics to be in Safe Areas defined by their own spec and standard.
Not just legals ...
....but the reason for the Standards does have everything to do with legals (and potential liabilties associated with them.)
After some lobbying, we in NZ have just had our Graphic Safe Area for HD revised from SD Safe to effectively 14:9 Safe Action. Area. (nearly )
Spec is now defined : HD 16:9 Graphics Safe is 70% of 16:9 width, 90% of Height
Image shows what we wanted and what we had ... but the spec as above is we got. It is fine.
Your second frame grab image is what I have achieved as well with these settings but I was hoping to get a setting that overlayed a single rectangle.
Not a biggie but just would have been "cleaner" to work with in AEFX.
Interestingly....I can achieve it easily in Premiere Pro though.
You can create any mask shape you like, apply stroke, then use it as a guide layer. Not as convient as PPro but EZ enough especially if you save it as an animation preset.
You can't eliminate double rectangles but you could set the Action Safe and Title Safe to 10% and Center Cut to 30% in Guides and Grids preferences. Would that be close enough???
Yep....thats what I had done.
It will do fine.