The other day I discovered a little trick to do just this - replace a pinned post with a link to another webpage.
All you need is the link to the pinned post and the link of what you want to replace the pinned post with. Then add this to your ‘Custom Javascript’:
var a = document.querySelector('a[href="https://blog.cjeller.site/search"]');
if (a) {
a.setAttribute('href', 'https://search.cjeller.site');
}
And off you pop! Might be a bit of a hack until more customization becomes available, but I think it does the job.