A Conservative is resistant to change - not against change. Conservatives like to think a proposal through (like a business executive) before going forth with change. It's just being cautious and thorough. Liberals sometimes misunderstand conservatives because conservatives don't move fast enough for them. Problem is, with so many special interest proposals put forth by liberals - conservatives get a headache with all the minutia and media pressure.
As for the meat of your question Conservative/Obstructionist, I disagree with your source definition of Conservative because in the middle phrase "tending to oppose change" the sub phrase "oppose change" is easily taken out of context. Here is my personal version defining conservative.
Conservative - champions preservation of society and culture. Not adverse to change, but averse to change (note the difference). And never to RAPID change.
As far as the comparison of Obstructionist goes, I can see that if you follow your definition of Conservative where you could easily make the connection. In reality though, both parties have their obstructionist political moves.
An obstructionist doesn't fool himself or anyone else about what the goal is. Conservatives think they must safe America by any means necessary.
American conservatism has grown into a cult.Everyone is out to get them and everything that's not slanted to the far right is liberally biased. Science,truth and facts are all less important than the ideology. Everyone who distracts from the Divine path becomes an enemy and part of the evil outside world. The few conservatives who are smart and courageous enough to make up their own mind are immediately labeled as traitors or RINO's It's good to see more and more Americans waking up and realizing they can't take conservatism serious anymore until it rids itself of this cultist spirit
an obstructionist tends to do things on purpose. I think many conservatives have a point. Though there are some things about this country which should be changed, a lot of it is working well.
It depends on the context. "Disposed to preserve existing conditions" does not mean the same as "deliberately delays or prevents progress". I suspect that you know that. Progress and change are not synonyms... as all change is not progressive.