------
## 最终结论
```python
def min_replacements_to_k_complete(t, test_cases):
    results = []
    for n, k, s in test_cases:
        changes = 0
        # We only need to check the first k positions and their corresponding period positions
        for i in range(k):
            # Collect characters at positions that should be equal
            count = [0] * 26
            total = 0
            j = i
            while j < n:
                count[ord(s[j]) - ord('a')] += 1
                total += 1
                j += k
            
            # Also consider the palindrome requirement
            j = n - i - 1
            while j >= n // 2:
                count[ord(s[j]) - ord('a')] += 1
                total += 1
                j -= k
            
            # Find the most frequent character in these positions
            max_freq = max(count)
            
            # Calculate minimum changes needed for this group of positions
            changes += (total // 2) - (max_freq // 2)
        
        results.append(changes)
    
    return results

# Example usage:
t = 4
test_cases = [
    (6, 2, "abaaba"),
    (6, 3, "abaaba"),
    (36, 9, "hippopotomonstrosesquippedaliophobia"),
    (21, 7, "wudixiaoxingxingheclp")
]

output = min_replacements_to_k_complete(t, test_cases)
for res in output:
    print(res)
```