At least, the first part does change game resolution to 800x600, I have also tried 1024x768 and 1152x864. It all worked, but since I was thinking about 800x600, I concentrated on this resolution.

For those interested, who are more advanced than me, this code might give some clues and hopefully allow for making the game run in higher resolutions.

Here are some notes:
_______________________
* Possible Reference to Dialog: DialogID_0068
|
:00417DB2 6A68 push 00000068
:00417DB4 8BD0 mov edx, eax
:00417DB6 59 pop ecx
:00417DB7 E8A49DFEFF call 00401B60

* Referenced by a (U)nconditional or ©onditional Jump at Addresses:
|:00417DA6(U), :00417DAA©
|
:00417DBC A1D4A15700 mov eax, dword ptr [0057A1D4]
:00417DC1 6A08 push 00000008
:00417DC3 6858020000 push 00000258 < game display height
:00417DC8 6820030000 push 00000320 < game display width
:00417DCD 8B08 mov ecx, dword ptr [eax]
:00417DCF 50 push eax
:00417DD0 FF5154 call [ecx+54]
:00417DD3 3BC3 cmp eax, ebx
:00417DD5 7437 je 00417E0E

* Reference To: USER32.GetSystemMetrics, Ord:012Ch
|
:00417DD7 8B3504924800 mov esi, dword ptr [00489204]
:00417DDD 53 push ebx
:00417DDE FFD6 call esi
:00417DE0 8BF8 mov edi, eax
:00417DE2 6A01 push 00000001
:00417DE4 FFD6 call esi
:00417DE6 8B0DD4A15700 mov ecx, dword ptr [0057A1D4]
:00417DEC 6A08 push 00000008
:00417DEE 50 push eax
:00417DEF 8B11 mov edx, dword ptr [ecx]
:00417DF1 57 push edi
:00417DF2 51 push ecx
:00417DF3 FF5254 call [edx+54]
:00417DF6 3BC3 cmp eax, ebx
:00417DF8 8B742410 mov esi, dword ptr [esp+10]
:00417DFC 7410 je 00417E0E
:00417DFE 68B7000000 push 000000B7
:00417E03 55 push ebp

* Possible Reference to Dialog: DialogID_0068
this changes in-game resolution to 800x600, but the image displayed is still 640x480...
=================================

:00407E7F B880020000 mov eax, 00000280 < X-axis width for mouse, 640 -> 800
:00407E84 3BF0 cmp esi, eax
:00407E86 7C02 jl 00407E8A
:00407E88 8BF0 mov esi, eax

* Referenced by a (U)nconditional or ©onditional Jump at Address:
|:00407E86©
|
:00407E8A 85FF test edi, edi
:00407E8C 7D02 jge 00407E90
:00407E8E 33FF xor edi, edi

* Referenced by a (U)nconditional or ©onditional Jump at Address:
|:00407E8C©
|
:00407E90 B8E0010000 mov eax, 000001E0 < Y-axis width for mouse, 480 -> 600
:00407E95 3BF8 cmp edi, eax
:00407E97 7C02 jl 00407E9B
:00407E99 8BF8 mov edi, eax
applied in x1
================================

:0041DEE3 6880020000 push 00000280 < changing this to 800 gives crash...

================================

the code below (very likely that its incomplete) affects screen display cery much!:
* Possible StringData Ref from Data Obj ->"SCROLLRT.cpp"
|
:0046ACA2 6870724B00 push 004B7270
:0046ACA7 BA470E0000 mov edx, 00000E47
:0046ACAC 8BCE mov ecx, esi
:0046ACAE E8D56DF9FF call 00401A88

* Referenced by a (U)nconditional or ©onditional Jump at Addresses:
|:0046ABF2©, :0046ACA0©
|
:0046ACB3 8B742410 mov esi, dword ptr [esp+10]
:0046ACB7 85F6 test esi, esi
:0046ACB9 7E0F jle 0046ACCA
:0046ACBB 56 push esi
:0046ACBC 6880020000 push 00000280 < 640 width, changing to 800 creates duplicate effect (like desktop tile)
:0046ACC1 33D2 xor edx, edx
:0046ACC3 33C9 xor ecx, ecx
:0046ACC5 E85B010000 call 0046AE25

* Referenced by a (U)nconditional or ©onditional Jump at Address:
|:0046ACB9©
|
:0046ACCA 81FEE0010000 cmp esi, 000001E0
:0046ACD0 0F8D11010000 jnl 0046ADE7
:0046ACD6 837C242400 cmp dword ptr [esp+24], 00000000
:0046ACDB BB65010000 mov ebx, 00000165
:0046ACE0 7413 je 0046ACF5
:0046ACE2 6A1C push 0000001C
:0046ACE4 68E8000000 push 000000E8
:0046ACE9 8BD3 mov edx, ebx
:0046ACEB B9CC000000 mov ecx, 000000CC
:0046ACF0 E830010000 call 0046AE25

* Referenced by a (U)nconditional or ©onditional Jump at Address:
|:0046ACE0©
|
:0046ACF5 837C241400 cmp dword ptr [esp+14], 00000000
:0046ACFA 7416 je 0046AD12
:0046ACFC 6A3C push 0000003C
:0046ACFE 6820010000 push 00000120
:0046AD03 BA8E010000 mov edx, 0000018E
:0046AD08 B9B0000000 mov ecx, 000000B0
:0046AD0D E813010000 call 0046AE25