How to replace a character in C# string ignoring other characters?

Question

You can rather use HttpUtility.HtmlEncode & HttpUtility.HtmlDecode like below.

First decode your string to get normal string and then encode it again which will give you expected string.

HttpUtility.HtmlEncode(HttpUtility.HtmlDecode("hello a & b, &lt;hello world &gt;"));

HttpUtility.HtmlDecode("hello a & b, <hello world >") will return hello a & b, <hello world >.
HttpUtility.HtmlEncode("hello a & b, <hello world >") will return hello a & b, <hello world >