Widening a patio door -- current door is an odd size

My patio door will need replacing soon. The rough opening is 64 inches wide. Now, patio doors come in the 5 or 6 foot flavour (give or take maybe one inch), am I correct? So is 64 inches too big for a 5 foot door and too small for a 6 foot door?
The easiest thing would be to make the opening smaller, but then I'd have to change the vinyl siding panels on the outside wall. If I widen, I can just cut it back. But that probably means I need to change the header of the RO. And obviously, a 6 foot door would be much nicer than a 5 foot. If I have to replace some siding (maybe the whole wall since that siding is probably 20 years old) it might be very expensive to actually downgrade to a smaller door.. :S
I'm not sure how much load the wall is bearing. It is a two story + basement home. The door is on the first floor. The floor and ceiling joists are parrallel with the wall and the I beam is perpendicular with the wall (about 3 feet away). That exterior wall (width of the house) is about 25 feet wide. The house is rectangular with no gables.
Would it be necessary to put up a temporary wall a few feet into the house to serve as a support while the header is replaced or is there an easier way? Would screwing a 2x6 across all the studs above the header be sufficient?
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snipped-for-privacy@gmail.com wrote:

Alternatively you could trim out around the door with some expanded PVC trim. You're only making up a couple or three inches on each side so wrapping trim around the opening would probably look just fine.

I've done it both ways. The first way is the standard way to do it and the only one I would recommend without actually seeing the situation in person.
R
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Have you tried to special order a new door the right size? I've done it many times (not that type of door), but it doesn't hurt to ask several places.
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I haven't looked into it yet. I want an idea of these alternatives first as I was told it would be a few hundred dollars more to get the custom size. If for those same few hundred dollars I can get a six foot door and not have to worry about the size next time it needs changing (by myself or future owners), then I would prefer to go that way.
Thanks for the suggestion, I may have to look into it..
snipped-for-privacy@gmail.com wrote:

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