Learn Dutch: Het was de bedoeling dat we de planning zouden veranderen. - The intention was that we would change the schedule.

This is the "future in the past" structure. Because the first part of the sentence is in the past (Het was), changing the schedule was a future action looking forward from that past moment. We show this by using zouden (the past tense of zullen, meaning "would") plus the infinitive veranderen.

Why are the verbs zouden and veranderen pushed to the very end?

The word dat (that) introduces a subclause. In a Dutch subclause, all verbs are pushed to the end of the sentence. Because of this, the helping verb zouden and the main verb veranderen both come after the object (de planning).

Can Het was de bedoeling dat... be translated simply as "We were supposed to..."?

Yes, absolutely! While it literally translates to "It was the intention that...", Dutch speakers use Het is/was de bedoeling dat... in the exact same way English speakers use "We are/were supposed to..." or "The plan is/was to...".

Does de planning refer to the action of planning?

Usually not. In Dutch, the loanword de planning is almost always used as a noun meaning "the schedule" or "the itinerary." If you want to talk about the action of making a plan, you would use the verb plannen.