Learn Finnish: Tätä asemakaavaa ei kuitenkaan hyväksyttäne. - This city plan, however, probably won't be approved.

First, find the passive stem. For hyväksyä, the passive is built on the strong grade stem hyväksyttä-. Then, add the potential passive marker -ne. Because this is a negative sentence, you do not add the final personal ending (which would be -en in the affirmative), leaving just hyväksyttäne after the negative verb ei.

How does the meaning change if we use the regular negative passive ei hyväksytä instead?

The sentence Tätä asemakaavaa ei hyväksytä uses the standard indicative mood, stating a direct fact: This city plan is not approved, or definitely will not be approved. Using the potential mood form ei hyväksyttäne adds uncertainty, shifting the meaning to probably will not be approved.

Why is tätä asemakaavaa in the partitive case here?

In Finnish passive sentences, the noun receiving the action is grammatically the object, even though it translates as the subject in the English passive voice. Because the verb in this sentence is negative (ei hyväksyttäne), the object must be placed in the partitive case.

Why does the word for however have a -kaan suffix here (kuitenkaan)?

The base word for however or anyway is kuitenkin. Whenever a sentence is negative, Finnish grammar requires you to replace the affirmative clitic -kin with its negative counterpart, -kaan (or -kään depending on vowel harmony).