Yes. You can make changes to your block template or callback function at any time. ACF Blocks are dynamic and are rendered by the server each time they are loaded. This allows changes to block templates to be applied to all existing block content.
Yes, but we recommend against it for performance reasons. Unlike loading a value from a post or user, block values are saved in the block HTML comment found within the post_content. This prevents the $post_id parameter from working as expected in our template functions. If you really need to, you can load the post_content of a given post, and then parse the blocks using the parse_blocks() function. As mentioned above, we do not recommend doing this as it will degrade site performance due to the large number of queries required.
Introduced in WordPress 5.0, the block-based editor “Gutenberg” has transformed the way content is created. Content is now created in the unit of blocks instead of freeform text. Blocks take various forms including Paragraphs, Headings, Media, and Embeds.