code:

[CmdletBinding(SupportsShouldProcess=$true)]
Param(
    [string]$SearchFileName,
    [string]$ReplacementFileName,
    [string]$SearchBase=".",
    [switch]$Rename
)
$originalFiles = Get-ChildItem -LiteralPath $SearchBase -Filter $SearchFileName -Recurse -File
foreach ($orgFile in $originalFiles) {
    Write-Verbose $orgFile.FullName
    if ($Rename) {
        Remove-Item -LiteralPath $orgFile.FullName
        Copy-Item -LiteralPath $ReplacementFileName -Destination $orgFile.DirectoryName
    } else {
        Copy-Item -LiteralPath $ReplacementFileName -Destination $orgFile.FullName
    }
}