Honestly it reads unnatural to me. Yet the Chinese language has so many varieties, the standard mandarin is so young and the written language had been separated from the oral for so long, the grammatical rules are sometimes determined by the authorities rather than naturally formed by the people who speak it. Thus I cannot say it’s truly ungrammatical for the standard mandarin or the written language.
Appositives are actually present in modern Chinese, no less than average languages. A trivial example is 我们二人. This should be accepted in most Chinese varieties, if not all. (Even 我俩 are appositives, 我 maintain its original first person plural pronoun reference, 俩 contextually refers to the same two persons including the speaker)
Appositives are usually succinct, compact, and syntactically simple, otherwise it could be structurally unclear. The use of 的 in both parts, 党的建设、新的伟大征程, break this pattern. The loose 定中结构 of both parts also contribute to it. For example, 她就是【我的数学老师王老师】, although the second part 王老师 is also 定中结构, it’s much simpler and compact. Native speakers will agree it’s grammatical and natural.
On the other hand, I don’t agree it’s appositives in your examples (though structurally both analyses are compatible, the use of 新的 largely determines my inclination). It’s clearer in this example which you think is structurally similar:
进行改革开放新的伟大革命
Linguistically, 新的伟大革命 can be interpreted an appositive of 改革开放, or alternatively 改革开放 locates it. Logically, 改革开放 started in 1978, though I don’t know when exactly your example is quoted from, it’s most likely that 改革开放 is no longer a NEW revolution by then.
党的建设新的伟大工程
may cause problem because of the use of two 的. It’s taken from a title so we’d better no say the wordy 党的建设当中的新的伟大工程. But honestly, I can’t come up with better ways to write it than the original quote.
The problem is still the loose structure of 党的建设. If we say 深入推进新时代党建新的伟大工程, then it’s clear. They don’t use it probably on purpose to appear more official. (similar to the use of full names rather than acronyms)
UPDATES
As I mentioned in the comments, since cases are not marked, sometimes the same words tolerant different grammatical analyses. So I read through the linked 2017 article to have a context. Interestingly, I think the two examples are actually in different structures.
我们党深刻认识到，实现中华民族伟大复兴，必须合乎时代潮流、顺应人民意愿，勇于改革开放，让党和人民事业始终充满奋勇前进的强大动力。我们党团结带领人民进行改革开放新的伟大革命，破除阻碍国家和民族发展的一切思想和体制障碍，开辟了中国特色社会主义道路，使中国大踏步赶上时代。
The party has lead other revolutions. The current and new one that we are experiencing now is 改革开放. IMO it's appositive in this case.
实现伟大梦想，必须建设伟大工程。这个伟大工程就是我们党正在深入推进的党的建设新的伟大工程。历史已经并将继续证明，没有中国共产党的领导，民族复兴必然是空想。我们党要始终成为时代先锋、民族脊梁，始终成为马克思主义执政党，自身必须始终过硬。全党要更加自觉地坚定党性原则，勇于直面问题，敢于刮骨疗毒，消除一切损害党的先进性和纯洁性的因素，清除一切侵蚀党的健康肌体的病毒，不断增强党的政治领导力、思想引领力、群众组织力、社会号召力，确保我们党永葆旺盛生命力和强大战斗力。
In this context, it's clear that 党的建设 modifies 伟大工程. All the sentences coming after describes "new projects" that suit the current time. Hard for me to put it in English, but 党的建设在新时代有了新的内涵. Just like umbrellas on a sunny day and those on a rainy day are different goods, 党的建设 in the old times and in the current times are different.
In this case, 党的建设当中的新的伟大工程 is not an equivalent expanding, and 党的建设这一新的伟大工程 is also problematic and not equivalent. I start to appreciate the beauty of the writing 党的建设新的伟大工程. I don't see any other option with the same style and under the current grammatical framework. The author is truly an artist of the language. Perhaps we have to leave the potential ambiguity to time for the natural evolution of the language to solve.
A long 定语 possibly with the help of 的 is a relatively new feature of Chinese, heavily influenced (not caused) by Mongolian. But Mongolian has strict case marking, direct migration of long 定语 doesn’t work well in Chinese. IMO, Chinese languages are still finding the most suitable way, in which process linguistically patterns like this are not widely recognized.
