Develop in a way that is easier to adapt to these changes, without having to edit the entire code if you need to change something

the problem:

Each trade has a value that indicates the transaction amount in dollars and a text indicating if the client´s sector is "Public" or "Private". They implement the following interface:
 
interface ITrade
{
    double Value { get; }
    string ClientSector { get; }
} 
 
Currently, there are three categories:
LOWRISK: Trades with value less than 1,000,000 and client from Public Sector
MEDIUMRISK: Trades with value greater than 1,000,000 and client from Public Sector
HIGHRISK: Trades with value greater than 1,000,000 and client from Private Sector
 
Imagine you receive a list of trades and you need to return a list of categories as below:
input:  List<ITrade> portfolio 
output: List<string> tradeCategories 
 
Example:
Input:
Trade1 {Value = 2000000; ClientSector = "Private"}
Trade2 {Value = 400000; ClientSector = "Public"}
Trade3 {Value = 500000; ClientSector = "Public"}
Trade4 {Value = 3000000; ClientSector = "Public"}
portfolio = {Trade1, Trade2, Trade3, Trade4} 
 
Output:
tradeCategories = {"HIGHRISK", "LOWRISK", "LOWRISK", "MEDIUMRISK"} 
 
Keep in mind that category rules may be added/removed/modified in the future and be highly complex.
Please write your answer in pseudo-code showing clearly what classes, interfaces, methods and design patterns you would create/use to solve this problem. Also, object oriented programming is appreciated. 

what I tried: I read this whole tutorial that explains what pseudo code is and uses java as an example: https://www.geeksforgeeks.org/how-to-write-a-pseudo-code/, but I don't know how to do it.

some code:  if (Trade.index(I).tradeValue < 1000000 and Trade.index(I).client ==< publicSector) Print (low risk)