In GN4, the format is a property of a linked text element, and not of a text frame. In other words, when you unlink an article from its frames, the frames do not keep the format. If you link another article to these frames, the elements of that article may be formatted differently.

An example: to a headline frame of 70pt high, was linked an article IRAQ (to-be-replaced article) with the 2 lines headline of 30pt, and the format of the headline was set to the 30A format. Now, you unlink the article IRAQ, and link to the same set of frames the article BUSH (replacement article), which head has the format 40B. The headline is therefore formatted with 40B, which may cause overset or underset in the replacement article.

You may want to keep in the replacement article the formats that were applied on the to-be-replaced article, to avoid the need to refit the article. This can be avoided by using the "replace article" procedure instead on unlinking manually.

Select all frames of the article to be replaced, and then on the Article menu, click Replace with another. When prompted, in the Select article dialog box, select the replacement article.

If the replacement article contains at least the same elements that were paginated in replaced article, it automatically appears on page:

If the replacement article contains less elements than the ones that were paginated in replaced article, you are prompted to add them to the replacement article. If you accept, the empty elements are added and linked to the related frames. If you decline, the elements are not added to the article, and the empty unlinked frames remain on the page.