Interesting use case, I am not sure if we are able to update via REST API but with CSOM you definitely can update Below
Below is using Powershell CSOM, but same can be used in C# or Javascript object model.
function Change-WebPart {
#variables that needs to be set before starting the script
$siteURL = "https://spfire.sharepoint.com"
$userName = "mpadmin@spfire.onmicrosoft.com"
$webURL = "https://spfire.sharepoint.com"
$relativePageUrl = "/SitePages/Home.aspx"
# Let the user fill in their password in the PowerShell window
$password = Read-Host "Please enter the password for $($userName)" -AsSecureString</pre>
# set SharePoint Online credentials
$SPOCredentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($userName, $password)
# Creating client context object
$context = New-Object Microsoft.SharePoint.Client.ClientContext($webURL)
$context.credentials = $SPOCredentials
#get Page file
$page = $context.web.getFileByServerRelativeUrl($relativePageUrl)
$context.load($page)
#send the request containing all operations to the server
try{
$context.executeQuery()
}
catch{
write-host "Error: $($_.Exception.Message)" -foregroundcolor red
}
#use the WebPartManger to load the webparts on a certain page
$webPartManager = $page.GetLimitedWebPartManager([System.Web.UI.WebControls.WebParts.PersonalizationScope]::Shared)
$context.load($webPartManager.webparts)
#send the request containing all operations to the server
try{
$context.executeQuery()
}
catch{
write-host "Error: $($_.Exception.Message)" -foregroundcolor red
}
#loop through all WebParts to get the correct one and change its property
foreach($webPartDefinition in $webpartmanager.webparts){
$context.Load($webPartDefinition.WebPart.Properties)
#send the request containing all operations to the server
try{
$context.executeQuery()
}
catch{
write-host "Error: $($_.Exception.Message)" -foregroundcolor red
}
#Only change the webpart with a certain title
if ($webPartDefinition.WebPart.Properties.FieldValues.Title -eq "Documents")
{
$webPartDefinition.webpart.properties["Title"] = "My Documents"
$webPartDefinition.SaveWebPartChanges()
}
}
}
Also sharing some other links for quick referece
https://www.sharepointfire.com/2016/04/editing-web-part-properties-with-powershell-csom-in-sharepoint/
https://sharepointsamurai.wordpress.com/2014/07/27/how-to-use-the-csom-to-update-sharepoint-web-part-properties/
below is using PnPcore
https://www.c-sharpcorner.com/article/working-with-web-part-properties/
