Massive differences between the two. The Soviets justified the Czechoslovak invasion by accusing Dubcek of taking Czechoslovakia from socialism altogether. In that regard, the invasion was marketed to prop up marxist socialism.
On the other hand, you're suggesting the Soviets invade Romania because the latter refused to give up land. Romania was still a communist country despite it's estrangement from Moscow.
While it didn't protect Czechoslovakia, being a member of the Warsaw pact would prevent such an escalation
You're suggesting an invasion during the 70s. By then, Romania's military was able to operate far more independently from the Warsaw Pact that it's neighbours. There would be no confusion as with Czechoslovakia that lead to their army practically giving up; it's clear that Romania is under siege.
The Soviets would get stiffer resistance than Operation Danube would have expected.
Lastly, the Soviets won't try this because it can open Pandora's box and backfire badly.
Well, I’m not suggesting that the Soviets just blatantly support the landgrab
Here’s my suggestions feel free to critique
1 soviets try to woo Ceausescu of Romania to come back Solidly in the soviet camp and break ties with China
2 if that fails, they start supporting separatist sentiment in Transylvania engineer, ethnic riots in the country
3 in the eastern bloc try to undermine the image of Ceausescu as an agent of the west and traitor
4 convince Bulgarian and Hungarian leaders that this is an opportunity of a lifetime to settle old scores with Romania ( even a people’s republic of Transylvania which is a Hungarian puppet could be an option)
5 try to find people within ruling Romanian elite who are willing to betray ceausescu
6 even if does come to full conflict with Romanian military, it was the not as advanced as many other members of WP. It might be bloodier than 1956 but there is a chance defections from within the party can weaken the resistance.
It can reignite territorial disputes within Eastern Europe yes but it can also show you cannot show the finger to USSR right in their backyard and get away with it